Photoactivated chemical bleaching of dyes

ABSTRACT

Methods comprising the use of photoactivated chemical bleaching for detecting multiple targets in a biological sample are provided. The methods include the steps of providing a biological sample containing multiple targets, binding at least one probe to one or more target present in the sample, and observing a signal from the probe. The method further includes the steps of contacting the sample comprising the bound probe with an electron transfer reagent and irradiating the sample, thereby initiating a photoreaction that substantially inactivates the probe by photoactivated chemical bleaching. The method further includes the steps of binding at least one probe to one or more target present in the sample, and observing a signal from the probe. The process of binding, observing and bleaching may be iteratively repeated.

BACKGROUND

Various methods may be used in biology and in medicine to observedifferent targets in a biological sample. For example, analysis ofproteins in histological sections and other cytological preparations maybe performed using the techniques of histochemistry,immunohistochemistry (IHC), or immunofluorescence. Analysis of proteinsin biological samples may also be performed using solid-stateimmunoassays, for example, using the techniques of western blots, orusing cell-based assays that can be performed, for example, by usingflow cytometry.

Many of the current techniques may detect only a few targets at one time(such as IHC or fluorescence-based Western blots where number of targetsdetectable is limited by the fluorescence-based detection system) in asingle sample. Further analysis of targets may require use of additionalbiological samples from the source, limiting the ability to determinerelative characteristics of the targets such as the presence, absence,concentration, and/or the spatial distribution of multiple biologicaltargets in the biological sample. Moreover, in certain instances, alimited amount of sample may be available for analysis or the individualsample may require further analysis.

Methods of iteratively analyzing an individual sample are described inU.S. Pat. No. 7,629,125 and U.S. Pat. No. 7,741,046. In particular, U.S.Pat. No. 7,741,046 provides methods of detecting multiple targets in abiological sample that involve the use of oxidation for inactivatingsignal generators (e.g., for bleaching fluorescent dyes.) The oxidationreaction is accomplished by using oxidizing reagents, such as hydrogenperoxide.

Additionally, a signal can be inactivated by continuous exposure of thesignal generator to irradiation, i.e., by photobleaching. Similar tosignal inactivation by oxidation, this process can be lengthy and maynot proceed to completion, resulting in reduced signal-to-noise ratio.In addition, continued exposure of sample to irradiation may damage thebiological sample. Thus, there still remains a need for faster, milderand more sensitive methods for sequential analysis of biologicaltargets.

BRIEF DESCRIPTION

Disclosed herein are novel methods for high-throughput multiplexingsample analysis. The methods employ, e.g., a signal cycling processwherein in each cycle, a photoreaction step allows the same signalgenerators, e.g., fluorophores, to be reused in the subsequent cycle todetect additional markers, e.g., proteins. These methods can beemployed, e.g., for sequentially analyzing a biological sample todiscern, among other things, the presence, absence, concentration,and/or spatial distribution of multiple biological targets in abiological sample. The photoreaction step can include applying anelectron transfer agent, e.g., a borate salt, and initiating aphotoreaction, e.g., by irradiating the sample with visible light, toinactivate the signal generator, e.g., fluorescent dye.

In some embodiments, advantages of the disclosed methods may include therapid destruction of signal in each cycle. For example, in someinstances, quenching is observed in about 20 seconds as compared to morethan 15 minutes in conventional methods. In some embodiments, thedisclosed methods also may be characterized by the absence of residualfluorescence even in high expression targets resulting, e.g., inincreased signal-to-noise ratio. Also, the disclosed methods do notdamage the biological sample or its components, e.g., the epitopes, suchthat the same sample may be used for many dozens of cycles. Also, insome embodiments, when compared to direct photobleaching of fluorescentdyes, the disclosed methods are advantageous because they do not requirehigh power light which may damage biological sample components.

In some embodiments, the present invention is a method of probingmultiple targets in a biological sample comprising:

-   -   (a) providing a biological sample containing multiple targets;    -   (b) binding at least one probe to one or more targets present in        the sample;    -   (c) observing a signal from the at least one probe bound in step        (b);    -   (d) contacting the sample comprising the bound probe of step (b)        with an electron transfer reagent;    -   (e) irradiating the sample of step (d);    -   (f) binding at least one probe to one or more targets present in        the sample of step (e); and    -   (g) observing a signal from the probe bound in step (f).

In some embodiments, the probe in step (b) comprises an optical signalgenerator, and the signal observed in step (c) is an optical signal. Infurther embodiments, the optical signal generator is a fluorescentsignal generator, and the optical signal observed in step (c) is afluorescent signal.

In some embodiments, step (b) includes binding more than one probe totwo or more targets.

In some embodiments, irradiating the sample in step (e) is carried outin the presence of a buffer. In some embodiments, irradiating is carriedout at pH 5-9. In some embodiments, irradiating is carried out at pH6-8.

In some embodiments, irradiating the sample in step (e) is carried outat the temperature of 4-50° C. In a preferred embodiment, irradiatingthe sample is carried out at the temperature of 20-30° C.

In some embodiments, irradiating the sample in step (e) is accomplishedby exposing the sample to light of 350 nm-1.3 μM in wavelength. In someembodiments, irradiating the sample is accomplished by exposing thesample to light of 400-700 nm in wavelength.

In some embodiments, the electron transfer reagent is a borate salt. Insome embodiments, the borate salt is represented by the followingstructural formula:

-   -   wherein:        -   each R₁, R₂, and R₃ is, independently, an alkyl, an alkenyl,            an akynyl, an aryl or a heteroaryl, wherein said alkyl,            alkenyl, alkynyl, aryl or heteroaryl is optionally            substituted with one or more substituents selected from the            group consisting of (C1-C4)alkyl, (C1-C4)alkoxy,            (C1-C4)alkylamino, amino, hydroxyl, cyano, halogen, or            nitro.        -   R₄ is an alkyl, an alkenyl, or an akynyl, wherein said            alkyl, alkenyl, or alkynyl is optionally substituted with            one or more substituents selected from the group consisting            of (C1-C4)alkyl, (C1-C4)alkoxy, (C1-C4)alkylamino, amino,            hydroxyl, cyano, halogen, or nitro, and        -   M⁺ is selected from the group consisting of organic and            inorganic cations.

In some embodiments, each R₁, R₂, and R₃ is aryl. In some embodiments,said aryl is phenyl. In some embodiments, said phenyl is anunsubstituted phenyl.

In some embodiments, R₄ is an optionally substituted alkyl. In someembodiments, R₄ is unsubstituted butyl.

In some embodiments, each R₁, R₂, and R₃ is an optionally substitutedaryl and R₄ is an optionally substituted alkyl. In a further embodiment,each R₁, R₂, and R₃ is unsubstituted phenyl and R₄ is unsubstitutedbutyl, and the borate salt is triphenylbutyl borate salt.

In some embodiments, M⁺ is an inorganic cation. In some embodiments, theinorganic cation is Li⁺, Na⁺ or K⁺.

In some embodiments, the probe comprises a binder and a signalgenerator. In some embodiments, the signal generator is a fluorescentsignal generator. In some embodiments, the fluorescent signal generatorcomprises a cyanine dye. In some embodiments, the cyanine dye is Cy3 orCy5.

In some embodiments, the cyanine dye is Cy3; irradiation of the samplein step (e) is accomplished by using optical filters, comprises exposingthe sample to light of 520-580 nm in wavelength; and results inselective photoexcitation of Cy3.

In some embodiments, the cyanine dye is Cy5; irradiation of the samplein step (e) is accomplished by using optical filters; comprises exposingthe sample to light of 620-680 nm in wavelength; and results inselective photoexcitation of Cy5.

In some embodiments, the biological sample in step (a) comprises cellorganelles, whole cells or tissue sections. In some embodiments, thesample comprises proteins, carbohydrates or nucleic acids.

In some embodiments, steps (d)-(g) are repeated one or more times. Insome embodiments, steps (d)-(g) are repeated at least 5, at least 15, atleast 30, at least 60, at least 100 or at least 150 times. In someembodiments, steps (d)-(g) are repeated 25-30 times. In otherembodiments, steps (d)-(g) are repeated 2-10 times.

In some embodiments, steps (d) and (e) are performed for about 20seconds to about 60 minutes. In some embodiments, steps (d) and (e) areperformed for about 20 seconds to about 15 minutes. In some embodiments,the steps (d) and (e) are performed for about 20 seconds to about 5minutes.

In some embodiments, steps (d) and (e) are performed at a temperature of4-50° C. In a preferred embodiment, the steps (d) and (e) are performedat a temperature of 20-30° C.

In some embodiments, the method also comprises measuring one or moreintensity values of the signal observed in observing step (c), step (g),or steps (c) and (g). In some embodiments, the method further comprisescorrelating the intensity value with an amount of target present in thesample.

In some embodiments, the probe in step (b) and the probe in step (f)each comprise a signal generator. In some embodiments, the signalgenerator in step (b) is the same as the signal generator in step (f).In other embodiments, the signal generator in step (b) is different fromthe signal generator in step (f).

In some embodiments, the signals observed in step (c) and step (g) areboth detectable in a single detection channel. In other embodiments, thesignal observed in step (c) or step (g) is independently detectable indifferent detection channels.

In some embodiments, the components of the biological sample that aredifferent from the probe are not significantly modified.

In some embodiments, no detectable signal is observed after step (e).

In some embodiments, the signal generator comprises a chromophore, or aRaman-active tag.

In some embodiments, the present invention is a method of probingmultiple targets in a biological sample comprising:

-   -   (a) providing a biological sample containing multiple targets;    -   (b) binding multiple probes to multiple targets present in the        sample;    -   (c) observing a first set of signals from the first set of        probes bound in step (b);    -   (d) contacting the sample comprising the bound probes of        step (b) with an electron transfer reagent;    -   (e) irradiating the sample of step (d);    -   (f) generating a second set of signals from the second set of        probes bound in step (b);    -   (g) observing the second set of signals.

In some embodiments, irradiation of sample in step (e) initiates aphotoreaction that substantially inactivates the signal generator byphotoactivated chemical bleaching. In some embodiments, thephotoreaction comprises intermolecular electron transfer. In otherembodiments, the photoreaction comprises intramolecular electrontransfer.

In some embodiments, the signal generator is irreversibly modified. Insome embodiments, the signal generator is irreversibly modified by aphotoreaction that inactivates the signal generator by photoactivatedchemical bleaching.

In some embodiments, the present invention is a high throughputmultiplexing biological sample analysis method, the method comprising:

-   -   a signal cycling process, wherein in each cycle, staining and        imaging is followed by applying an electron transfer reagent and        irradiation of the biological sample.

In some embodiments, the method allows rapid signal cycling withoutsignificantly modifying the components of the biological sample that aredifferent from the probe.

In some embodiments, the present invention is a kit for probing multipletargets in a biological sample comprising:

-   -   multiple probes comprising a binder coupled to a signal        generator;    -   an electron transfer reagent that, when contacted with the        signal generator is capable of bleaching the signal generator        upon irradiation.

In some embodiments, the present invention is a series of at least twoimages depicting optically labeled biological targets wherein:

-   -   the images are obtained in the process of probing multiple        targets in a biological sample, wherein the process comprises:        -   (a) providing a biological sample containing multiple            targets;        -   (b) binding at least one optical probe to one or more            targets present in the sample;        -   (c) observing a signal from the optical probe bound in step            (b);        -   (d) contacting the sample comprising the bound optical probe            of step (b) with an electron transfer reagent;        -   (e) irradiating the sample of step (d);        -   (f) binding at least one optical probe to one or more            targets present in the sample of step (e); and        -   (g) observing a signal from the optical probe bound in step            (f).

In some embodiments, the present invention is a method of probingtargets in a biological sample comprising:

-   -   (a) providing a biological sample containing multiple targets;    -   (b) binding at least one probe to one or more targets present in        the sample;    -   (c) observing a signal from the probe bound in step (b);    -   (d) contacting the sample comprising the bound probe of step (b)        with an electron transfer reagent; and    -   (e) irradiating the sample of step (d).

In some embodiments, the present invention is a method of probingmultiple targets in a biological sample comprising:

-   -   (a) providing a biological sample containing multiple targets;    -   (b) binding at least one probe to one or more targets present in        the sample;    -   (c) binding at least one control probe to one or more targets        present in the sample;    -   (d) observing a signal from the probe bound in step (b) and a        control signal from the control probe bound in step (c);    -   (e) contacting the sample in step (d) with an electron transfer        reagent that is capable of selectively reacting with the probe        and not the control probe;    -   (f) irradiating the sample of step (e)    -   (g) binding at least one probe to one or more targets present in        the sample of step (f); and    -   (h) observing a signal from the probe bound in step (h).

In some embodiments, the steps (b) and (c) are performed simultaneously.In some embodiments, the step (h) also comprises observing a signal fromthe control probe bound in step (c).

DESCRIPTION OF THE FIGURES

FIG. 1 is a grayscale image of a graph showing absorbance of Cy3 dye at550 nm after incubation with different concentrations of triphenylbutylborate lithium salt and irradiation for 4 or 10 minutes.

FIG. 2 is a grayscale image of vials containing Cy3 dye before and afterphotoactivated chemical bleaching or thermal oxidation. Also shown is avial containing a control solution of Cy3 in water.

FIG. 3 shows grayscale images of samples stained with Cy3-conjugatedcytokeratin before and after photoactivated chemical bleaching.

FIG. 4 shows grayscale images of samples stained with Cy5-conjugated pancadherin before and after photoactivated chemical bleaching.

FIG. 5 shows a grayscale image of vials containing BODIPY dye before andafter photoactivated chemical bleaching. FIG. 5 also shows a grayscaleimage of fluorescence spectrum of BODIPY dye before and afterphotoactivated chemical bleaching.

FIG. 6 shows a grayscale image of vials containing a rhodamine dyebefore and after photoactivated chemical bleaching. FIG. 6 also shows agrayscale image of a fluorescence spectrum of rhodamine dye before andafter photoactivated chemical bleaching.

FIG. 7 shows a grayscale image of vials containing1,3-dichloro-7-hydroxy-9,9-dimethyl-2(9H)-Acridinone (DDAO) dye beforeand after photoactivated chemical bleaching.

FIG. 7 also shows a grayscale image of a fluorescence spectrum of1,3-dichloro-7-hydroxy-9,9-dimethyl-2(9H)-Acridinone (DDAO) dye beforeand after photoactivated chemical bleaching.

DETAILED DESCRIPTION Definitions

The singular forms “a” “an” and “the” include plural referents unlessthe context clearly dictates otherwise. Approximating language, as usedherein throughout the specification and claims, may be applied to modifyany quantitative representation that could permissibly vary withoutresulting in a change in the basic function to which it is related.Accordingly, a value modified by a term such as “about” is not to belimited to the precise value specified. Unless otherwise indicated, allnumbers expressing quantities of ingredients, properties such asmolecular weight, reaction conditions, so forth used in thespecification and claims are to be understood as being modified in allinstances by the term “about.” Accordingly, unless indicated to thecontrary, the numerical parameters set forth in the followingspecification and attached claims are approximations that may varydepending upon the desired properties sought to be obtained by thepresent invention. At the very least each numerical parameter should atleast be construed in light of the number of reported significant digitsand by applying ordinary rounding techniques.

As used herein, the term “alkyl” refers to saturated aliphatic groups,including straight-chain alkyl groups (e.g., methyl, ethyl, propyl,butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, etc.), branched-chainalkyl groups (isopropyl, tert-butyl, isobutyl, etc.). In certainembodiments, a straight chain or branched chain alkyl has 6 or fewercarbon atoms in its backbone (e.g., C₁-C₆ for straight chain, C₃-C₆ forbranched chain) or 4 or fewer carbon atoms in its backbone (e.g., C₁-C₄for straight chain, C₃-C₄ for branched chain). The term “C₁-C₆”alkylrefers to alkyl groups containing 1 to 6 carbon atoms. The term“C₁-C₄”alkyl refers to alkyl groups containing 1 to 4 carbon atoms.Moreover, the term alkyl includes both “unsubstituted alkyls” and“substituted alkyls,” the latter of which refers to alkyl moietieshaving substituents replacing a hydrogen on one or more carbons of thehydrocarbon backbone. Such substituents can include, for example,(C1-C4)alkyl, (C1-C4)alkoxy, amino (including (C1-C4) alkylamino and(C1-C4)dialkylamino), hydroxyl, cyano, halogen, or nitro. Cycloalkylscan be further substituted, e.g., with the substituents described above.

As used herein, the term “alkenyl” refers to unsaturated aliphaticgroups analogous in length and possible substitution to the alkylsdescribed above, but that contain at least one double bond. For example,the term “alkenyl” includes straight-chain alkenyl groups (e.g.,ethylenyl, propenyl, butenyl, pentenyl, hexenyl, heptenyl, octenyl,nonenyl, decenyl, etc.), branched-chain alkenyl groups. Moreover, theterm “alkenyl” includes both “unsubstituted alkenyls” and “substitutedalkenyls,” the latter of which refers to alkenyl moieties havingsubstituents replacing a hydrogen on one or more carbons of thehydrocarbon backbone. Such substituents can include, for example,(C1-C4)alkyl, (C1-C4)alkoxy, amino (including (C1-C4)alkylamino and(C1-C4)dialkylamino), hydroxyl, cyano, halogen, or nitro.

As used herein, the term “alkynyl” refers to unsaturated aliphaticgroups analogous in length and possible substitution to the alkylsdescribed above, but which contain at least one triple bond. Forexample, the term “alkynyl” includes straight-chain alkynyl groups(e.g., ethynyl, propynyl, butynyl, pentynyl, hexynyl, heptynyl, octynyl,nonynyl, decynyl, etc.), or branched-chain alkynyl groups. Moreover, theterm “alkynyl” includes both “unsubstituted alkynyls” and “substitutedalkynyls,” the latter of which refers to alkynyl moieties havingsubstituents replacing a hydrogen on one or more carbons of thehydrocarbon backbone. Such substituents can include, for example,(C1-C4)alkyl, (C1-C4)alkoxy, amino (including (C1-C4)alkylamino and(C1-C4)dialkylamino), hydroxyl, cyano, halogen, or nitro.

As used herein, the term “alkoxy” refers to substituted andunsubstituted alkyl, alkenyl, and alkynyl groups covalently linked to anoxygen atom. Examples of alkoxy groups include, but are not limited to,methoxy, ethoxy, isopropyloxy, propoxy, butoxy, and pentoxy groups. Incertain embodiments, a straight chain or branched chain alkoxy has 4 orfewer carbon atoms in its backbone (e.g., C1-C4 for straight chain,C3-C4 for branched chain). The term “C1-C4”alkyl refers to alkyl groupscontaining 1 to 4 carbon atoms.

As used herein, the term “amine” or “amino” refers to compounds orsubstituents where a nitrogen atom is covalently bonded to at least onecarbon or heteroatom. The term includes “alkyl amino” which comprisesgroups and compounds wherein: the nitrogen is bound to at least oneadditional alkyl group. The term “dialkyl amino” includes groupswherein: the nitrogen atom is bound to at least two additional alkylgroups. In certain embodiments, these alkyl groups have 4 or fewercarbon atoms in their backbone (e.g., C₁-C₄ for straight chain, C₃-C₄for branched chain). The term (C1-C4)alkylamino refers to groups andcompounds, wherein the nitrogen is bound to at least one additionalC1-C4 alkyl group. The term “(C1-C4)dialkylamino refers to groups andcompounds, wherein the nitrogen is bound to at least two additionalC1-C4 alkyl groups.

As used herein, the term “aryl” refers to groups, e.g., 5- and6-membered single-ring aromatic groups, that may include from zero tofour heteroatoms, for example, benzene, phenyl, pyrrole, furan,thiophene, thiazole, isothiaozole, imidazole, triazole, tetrazole,pyrazole, oxazole, isooxazole, pyridine, pyrazine, pyridazine, andpyrimidine, and the like. Furthermore, the term “aryl” includesmulticyclic aryl groups, e.g., tricyclic, bicyclic, e.g., naphthalene,benzoxazole, benzodioxazole, benzothiazole, benzoimidazole,benzothiophene, methylenedioxyphenyl, quinoline, isoquinoline,napthridine, indole, benzofuran, purine, benzofuran, deazapurine, orindolizine. Those aryl groups having heteroatoms in the ring structuremay also be referred to as “aryl heterocycles,” “heteroaryls” or“heteroaromatics.” The aromatic ring can be substituted at one or morering positions with such substituents as described above, as forexample, (C1-C4)alkyl, (C1-C4)alkoxy, amino (including (C1-C4)alkylaminoand (C1-C4)dialkylamino), hydroxyl, cyano, halogen, or nitro. Arylgroups can also be fused or bridged with alicyclic or heterocyclic ringswhich are not aromatic so as to form a polycycle (e.g., tetralin). Theterm heteroaryl includes unsaturated cyclic compounds such as azirine,oxirene, dithiete, pyrroline, pyrrole, furan, dihydrofuran,dihydrothiophene, thiophene, pyrazole, imidazole, oxazole, thiazole,isothiazole, 12,2,3-triazole, 1,2,4, triazole, dithiazole, tetrazole,pyridine, pyran, pyrimidine, pyran, thiapyrane, diazine, thiazine,dioxine, triazine and tetrazene.

As used herein, the term “antibody” refers to an immunoglobulin thatspecifically binds to and is thereby defined as complementary with aparticular spatial and polar organization of another molecule. Theantibody may be monoclonal or polyclonal and may be prepared bytechniques that are well known in the art such as immunization of a hostand collection of sera (polyclonal), or by preparing continuous hybridcell lines and collecting the secreted protein (monoclonal), or bycloning and expressing nucleotide sequences or mutagenized versionsthereof, coding at least for the amino acid sequences required forspecific binding of natural antibodies. Antibodies may include acomplete immunoglobulin or fragment thereof, which immunoglobulinsinclude the various classes and isotypes, such as IgA, IgD, IgE, IgG1,IgG2a, IgG2b and IgG3, IgM. Functional antibody fragments may includeportions of an antibody capable of retaining binding at similar affinityto full-length antibody (for example, Fab, Fv and F(ab′).sub.2, orFab′). In addition, aggregates, polymers, and conjugates ofimmunoglobulins or their fragments may be used where appropriate so longas binding affinity for a particular molecule is substantiallymaintained.

As used herein, the term “binder” refers to a molecule that may bind toone or more targets in the biological sample. A binder may specificallybind to a target. Suitable binders may include one or more of natural ormodified peptides, proteins (e.g., antibodies, affibodies, or aptamers),nucleic acids (e.g., polynucleotides, DNA, RNA, or aptamers);polysaccharides (e.g., lectins, sugars), lipids, enzymes, enzymesubstrates or inhibitors, ligands, receptors, antigens, or haptens. Asuitable binder may be selected depending on the sample to be analyzedand the targets available for detection. For example, a target in thesample may include a ligand and the binder may include a receptor or atarget may include a receptor and the binder may include a ligand.Similarly, a target may include an antigen and the binder may include anantibody or antibody fragment or vice versa. In some embodiments, atarget may include a nucleic acid and the binder may include acomplementary nucleic acid. In some embodiments, both the target and thebinder may include proteins capable of binding to each other.

As used herein, the term “biological sample” refers to a sample obtainedfrom a biological subject, including sample of biological tissue orfluid origin obtained in vivo or in vitro. Such samples can be, but arenot limited to, body fluid (e.g., blood, blood plasma, serum, or urine),organs, tissues, fractions, cells isolated from mammals including,humans and cell organelles. Biological samples also may include sectionsof the biological sample including tissues (e.g., sectional portions ofan organ or tissue). Biological samples may also include extracts from abiological sample, for example, an antigen or a nucleic acid from abiological fluid (e.g., blood or urine). Biological samples may compriseproteins, carbohydrates or nucleic acids.

A biological sample may be of prokaryotic origin, archaeal origin, oreukaryotic origin (e.g., insects, protozoa, birds, fish, reptiles). Insome embodiments, the biological sample is mammalian (e.g., rat, mouse,cow, dog, donkey, guinea pig, or rabbit). In certain embodiments, thebiological sample is of primate origin (e.g., example, chimpanzee, orhuman).

As used herein, the term “control probe” refers to an agent having abinder coupled to a signal generator or a signal generator capable ofstaining directly, such that the signal generator retains at least 80percent signal after contact with an electron transfer reagent andsubsequent irradiation. A suitable signal generator in a control probeis not substantially inactivated, e.g., substantially bleached byphotoactivated chemical bleaching, when contacted with the electrontransfer reagent and irradiated. Suitable examples of signal generatorsmay include a fluorophore that does not undergo bleaching under theconditions employed (e.g., DAPI).

As used herein, the term “enzyme” refers to a protein molecule that cancatalyze a chemical reaction of a substrate. In some embodiments, asuitable enzyme catalyzes a chemical reaction of the substrate to form areaction product that can bind to a receptor (e.g., phenolic groups)present in the sample. A receptor may be exogeneous (that is, a receptorextrinsically adhered to the sample or the solid-support) or endogeneous(receptors present intrinsically in the sample or the solid-support).Examples of suitable enzymes include peroxidases, oxidases,phosphatases, esterases, and glycosidases. Specific examples of suitableenzymes include horseradish peroxidase, alkaline phosphatase,β-D-galactosidase, lipase, and glucose oxidase.

As used herein, the term “enzyme substrate” refers to a chemicalcompound that is chemically catalyzed by an enzyme to form a reactionproduct. In some embodiments, the reaction product is capable of bindingto a receptor present in the sample. In some embodiments, enzymesubstrates employed in the methods herein may include non-chromogenic ornon-chemiluminescent substrates. A signal generator may be attached tothe enzyme substrate as a label.

As used herein, the term “electron transfer reagent” refers to a reagentthat can engage in a photoreaction with a molecule capable of undergoingphotoexcitation. This term also refers to a composition comprising areagent that can engage in a photoreaction with a molecule capable ofundergoing photoexcitation. In some embodiments, the molecule capable ofundergoing photoexcitation may be a signal generator. In someembodiment, the electron transfer reagent may donate an electron to thesignal generator in the course of a photoreaction. In alternativeembodiments, the electron transfer reagent may accept an electron fromthe signal generator in the course of a photoreaction.

In some embodiments, the electron transfer reagent donating an electronto the signal generator in the course of a photoreaction may be a boratesalt. In a further embodiment, the borate salt is triphenylbutyl borate.

In alternative embodiments, the electron transfer reagent accepting anelectron from the photoexcited molecule may be an onium salt [e.g.,diphenyliodonium hexafluorophosphate (DPI) or dimethylphenacylsulfoniumtetrafluoroborate (DMPS)], or tetrabutylammonium butyltriphenylborate(TBAB).

As used herein, the term “fluorophore” or “fluorescent signal generator”refers to a chemical compound, which when excited by exposure to aparticular wavelength of light, emits light at a different wavelength.Fluorophores may be described in terms of their emission profile, or“color.” Green fluorophores (for example Cy3, FITC, and Oregon Green)may be characterized by their emission at wavelengths generally in therange of 515-540 nanometers. Red fluorophores (for example Texas Red,Cy5, and tetramethylrhodamine) may be characterized by their emission atwavelengths generally in the range of 590-690 nanometers. Examples offluorophores include, but are not limited to,4-acetamido-4′-isothiocyanatostilbene-2,2′ disulfonic acid, acridine,derivatives of acridine and acridine isothiocyanate,5-(2′-aminoethyl)aminonaphthalene-1-sulfonic acid (EDANS),4-amino-N-[3-vinylsulfonyl)phenyl]naphthalimide-3,5 disulfonate (LuciferYellow VS), N-(4-anilino-1-naphthyl)maleimide, anthranilamide, BrilliantYellow, coumarin, coumarin derivatives, 7-amino-4-methylcoumarin (AMC,Coumarin 120), 7-amino-trifluoromethylcouluarin (Coumaran 151),cyanosine; 4′,6-diaminidino-2-phenylindole (DAPI),5′,5″-dibromopyrogallol-sulfonephthalein (Bromopyrogallol Red),7-diethylamino-3-(4′-isothiocyanatophenyl)-4-methylcoumarin, -,4,4′-diisothiocyanatodihydro-stilbene-2,2′-disulfonic acid,4,4′-diisothiocyanatostilbene-2,2′-disulfonic acid,5-[dimethylamino]naphthalene-1-sulfonyl chloride (DNS, dansyl chloride),fluorescein and derivatives such as 5-carboxyfluorescein (FAM),5-(4,6-dichlorotriazin-2-yl)aminofluorescein (DTAF),2′7′-dimethoxy-4′5′-dichloro-6-carboxyfluorescein (JOE), fluorescein,fluorescein isothiocyanate (FITC), QFITC (XRITC); fluorescaminederivative (fluorescent upon reaction with amines); IR144; IR1446;Malachite Green isothiocyanate; 4-methylumbelliferone; orthocresolphthalein; nitrotyrosine; pararosaniline; Phenol Red,B-phycoerythrin; o-phthaldialdehyde derivative (fluorescent uponreaction with amines); pyrene and derivatives such as pyrene, pyrenebutyrate and succinimidyl 1-pyrene butyrate; Reactive Red 4 (Cibacron®Brilliant Red 3B-A), rhodamine and derivatives such as6-carboxy-X-rhodamine (ROX), 6-carboxyrhodamine (R6G), lissaminerhodamine B sulfonyl chloride, rhodamine (Rhod), rhodamine B, rhodamine123, rhodamine X isothiocyanate, sulforhodamine B, sulforhodamine 101and sulfonyl chloride derivative of sulforhodamine 101 (Texas Red);N,N,N′,N′-tetramethyl-6-carboxyrhodamine (TAMRA); tetramethyl Rhodamine,tetramethyl rhodamine isothiocyanate (TRITC); riboflavin; rosolic acidand lathanide chelate derivatives, cyanines, pyrelium dyes, squaraines,1,3-dichloro-7-hydroxy-9,9-dimethyl-2(9H)-Acridinone (DDAO), anddimethylacridinone (DAO). In some embodiments, the fluorophore can becyanine, rhodamine, BODIPY or1,3-dichloro-7-hydroxy-9,9-dimethyl-2(9H)-Acridinone (DDAO) dyes. In apreferred embodiment, the fluorophore is a cyanine dye. In a furtherembodiment, the cyanine dye is Cy3 or Cy5.

As used herein, the term “in situ” generally refers to an eventoccurring in the original location, for example, in intact organ ortissue or in a representative segment of an organ or tissue. In someembodiments, in situ analysis of targets may be performed on cellsderived from a variety of sources, including an organism, an organ,tissue sample, or a cell culture. In situ analysis provides contextualinformation that may be lost when the target is removed from its site oforigin. Accordingly, in situ analysis of targets describes analysis oftarget-bound probe located within a whole cell or a tissue sample,whether the cell membrane is fully intact or partially intact wheretarget-bound probe remains within the cell. Furthermore, the methodsdisclosed herein may be employed to analyze targets in situ in cell ortissue samples that are fixed or unfixed.

As used herein, the terms “irradiation” or “irradiate” refer to act orprocess of exposing a sample or a solution to non-ionizing radiation. Insome embodiments, the non-ionizing irradiation has wavelengths between350 nm and 1.3 μm. In preferred embodiments, the non-ionizing radiationis visible light of 400-700 nm in wavelength. Irradiation may beaccomplished by exposing a sample or a solution to a radiation source,e.g., a lamp, capable of emitting radiation of a certain wavelength or arange of wavelengths. In some embodiments, a molecule capable ofundergoing photoexcitation is photoexcited as a result of irradiation.In some embodiments, the molecule capable of undergoing photoexcitationis a signal generator, e.g., a fluorescent signal generator. In someembodiments, irradiation of a fluorescent signal generator initiates aphotoreaction between the fluorescent signal generator and the electrontransfer reagent. In some embodiments, irradiation initiates aphotoreaction substantially inactivates the signal generator byphotoactivated chemical bleaching.

Optical filters may be used to restrict irradiation of a sample or asolution to a particular wavelength or a range of wavelengths. In someembodiments, the optical filters may be used to restrict irradiation toa narrow range of wavelengths for selective photoexcitation of one ormore molecules capable of undergoing photoexcitation. The term“selective photoexcitation” refers to an act or a process, whereby oneor more molecules capable of undergoing photoexcitation are photoexcitedin the presence of one or more other molecules capable of undergoingphotoexcitation that remain in the ground electronic state afterirradiation.

In some embodiments, the molecule capable of undergoing photoexcitationis a fluorescent dye, e.g., a cyanine dye. In one further embodiment,irradiation limited to a range of wavelengths between 520-580 nm is usedfor selective photoexciation of a Cy3 dye. In another furtherembodiment, irradiation limited to a range of wavelengths between620-680 nm is used for selective photoexcitation of a Cy5 dye. Inalternative embodiments, irradiation of a sample at a specificwavelength may also be accomplished by using a laser.

As used herein, the term “peroxidase” refers to an enzyme class thatcatalyzes an oxidation reaction of an enzyme substrate along with anelectron donor. Examples of peroxidase enzymes include horseradishperoxidase, cytochrome C peroxidase, glutathione peroxidase,microperoxidase, myeloperoxidase, lactoperoxidase, or soybeanperoxidase.

As used herein, the term “peroxidase substrate” refers to a chemicalcompound that is chemically catalyzed by peroxidase to form a reactionproduct. In some embodiments, peroxidase substrates employed in themethods herein may include non-chromogenic or non-chemiluminescentsubstrates. A fluorescent signal generator may be attached to theperoxidase substrate as a label.

As used herein, the term “bleaching”, “photoactivated chemicalbleaching” or “photoinduced chemical bleaching” refers to an act or aprocess whereby a signal generated by a signal generator is modified inthe course of a photoreaction. In certain embodiments, the signalgenerator is irreversibly modified.

In some embodiments, the signal is diminished or eliminated as a resultof photoactivated chemical bleaching. In some embodiments, the signalgenerator is completely bleached, i.e., the signal intensity decreasesby about 100%. In some embodiments, the signal is an optical signal, andthe signal generator is an optical signal generator. The term“photoactivated chemical bleaching” is meant to exclude photobleaching,or loss of signal (e.g., fluorescent signal) that may occur in theabsence of electron transfer reagent, e.g., after continued irradiationof a signal generator, such as a fluorophore, or after its continuedexposure to light.

As used herein, the term “photoexcitation” refers to an act or a processwhereby a molecule transitions from a ground electronic state to anexcited electronic state upon absorption of radiation energy, e.g. uponirradiation. Photoexcited molecules can participate in chemicalreactions, e.g., in electron transfer reactions. In some embodiments, amolecule capable of undergoing photoexcitation is a signal generator,e.g., a fluorescent signal generator.

As used herein, the term “photoreaction” or a “photoinduced reaction”refers to a chemical reaction that is initiated and/or proceeds as aresult of photoexcitation of at least one reactant. The reactants in aphotoreaction may be an electron transfer reagent and a molecule capableof undergoing photoexcitation. In some embodiments, a photoreaction mayinvolve an electron transfer from the electron transfer reagent to themolecule that has undergone photoexcitation, i.e., the photoexcitedmolecule. In alternative embodiments, a photoreaction may also involvean electron transfer from the molecule that has undergonephotoexcitation to the electron transfer reagent. In some embodiments,the molecule capable of undergoing photoexcitation is a fluorescentsignal generator, e.g., a fluorophore. In some embodiments,photoreaction results in irreversible modification of one or morecomponents of the photoreaction. In some embodiments, photoreactionsubstantially inactivates the signal generator by photoactivatedchemical bleaching.

In some embodiments, the photoreaction may involve in intermolecularelectron transfer between the electron transfer reagent and thephotoexcited molecule, e.g., the electron transfer occurs when thelinkage between the electron transfer reagent and the photoexcitedmolecule is transitory, forming just prior to the electron transfer anddisconnecting after electron transfer.

In some embodiments, the photoreaction may involve intramolecularelectron transfer between the electron transfer reagent and thephotoexcited molecule, e.g. the electron transfer occurs when theelectron transfer reagent and the photoexcited molecule have been linkedtogether, e.g., by covalent or electrostatic interactions, prior toinitiation of the electron transfer process. The photoreaction involvingthe intramolecular electron transfer can occur, e.g., when the moleculecapable of undergoing photoexcitation and the electron transfer reagentcarry opposite charges and form a complex held by electrostaticinteractions. For example, a cationic dye, e.g., a cationic cyanine dyeand triphenylbutyl borate anion may form a complex, whereinintramolecular electron transfer may occur between the cyanine andborate moieties upon irradiation.

As used herein, the term “probe” refers to an agent having a binder anda label, such as a signal generator or an enzyme. In some embodiments,the binder and the label (signal generator or the enzyme) are embodiedin a single entity. The binder and the label may be attached directly(e.g., via a fluorescent molecule incorporated into the binder) orindirectly (e.g., through a linker) and applied to the biological samplein a single step. In alternative embodiments, the binder and the labelare embodied in discrete entities (e.g., a primary antibody capable ofbinding a target and an enzyme or a signal generator-labeled secondaryantibody capable of binding the primary antibody). When the binder andthe label (signal generator or the enzyme) are separate entities theymay be applied to a biological sample in a single step or multiplesteps. As used herein, the term “fluorescent probe” refers to an agenthaving a binder coupled to a fluorescent signal generator. In someembodiments, the probe may comprise an optical signal generator, suchthat the signal observed is an optical signal. In some embodiments, theprobe may comprise a fluorescent signal generator, such that the signalobserved is a fluorescent signal.

As used herein, the term “signal generator” refers to a molecule capableof providing a detectable signal using one or more detection techniques(e.g., spectrometry, calorimetry, spectroscopy, or visual inspection).Suitable examples of a detectable signal may include an optical signal,and electrical signal. Examples of signal generators include one or moreof a chromophore, a fluorophore, or a Raman-active tag. As stated above,with regard to the probe, the signal generator and the binder may bepresent in a single entity (e.g., a target binding protein with afluorescent label) in some embodiments. Alternatively, the binder andthe signal generator may be discrete entities (e.g., a receptor proteinand a labeled-antibody against that particular receptor protein) thatassociate with each other before or upon introduction to the sample.

In some embodiments, the signal generator may be an optical signalgenerator. In some embodiments, the optical signal generator may be afluorescent signal generator, e.g., a fluorophore. In preferredembodiments, the fluorescent signal generator may be a cyanine dye,e.g., Cy3, Cy5 or Cy7. In some embodiments, the signal generator, e.g.,a fluorophore, may be charged. In one embodiment, the signal generatoris a cationic fluorescent dye.

As used herein, the term “solid support” refers to an article on whichtargets present in the biological sample may be immobilized andsubsequently detected by the methods disclosed herein. Targets may beimmobilized on the solid support by physical adsorption, by covalentbond formation, or by combinations thereof. A solid support may includea polymeric, a glass, or a metallic material. Examples of solid supportsinclude a membrane, a microtiter plate, a bead, a filter, a test strip,a slide, a cover slip, and a test tube.

As used herein, the term “specific binding” refers to the specificrecognition of one of two different molecules for the other compared tosubstantially less recognition of other molecules. The molecules mayhave areas on their surfaces or in cavities giving rise to specificrecognition between the two molecules arising from one or more ofelectrostatic interactions, hydrogen bonding, or hydrophobicinteractions. Specific binding examples include, but are not limited to,antibody-antigen interactions, enzyme-substrate interactions,polynucleotide interactions, and the like. In some embodiments, a bindermolecule may have an intrinsic equilibrium association constant (K_(A))for the target no lower than about 10⁵ M⁻¹ under ambient conditions suchas a pH of about 6 to about 8 and temperature ranging from about 0° C.to about 37° C.

As used herein, the term “target” refers to the component of abiological sample that may be detected when present in the biologicalsample. The target may be any substance for which there exists anaturally occurring specific binder (e.g., an antibody), or for which aspecific binder may be prepared (e.g., a small molecule binder or anaptamer). In general, a binder may bind to a target through one or morediscrete chemical moieties of the target or a three-dimensionalstructural component of the target (e.g., 3D structures resulting frompeptide folding). The target may include one or more of natural ormodified peptides, proteins (e.g., antibodies, affibodies, or aptamers),nucleic acids (e.g., polynucleotides, DNA, RNA, or aptamers);polysaccharides (e.g., lectins or sugars), lipids, enzymes, enzymesubstrates, ligands, receptors, antigens, or haptens. In someembodiments, targets may include proteins or nucleic acids.

The invention includes embodiments that relate generally to methodsapplicable in analytical, diagnostic, or prognostic applications such asanalyte detection, fluorescence-activated cell sorting (FACS),histochemistry, immunohistochemistry, or immunofluorescence. In someembodiments, the methods disclosed herein may be particularly applicablein histochemistry, immunostaining, immunohistochemistry, immunoassays,or immunofluorescence. In some embodiments, the methods disclosed hereinmay be particularly applicable in immunoblotting techniques, forexample, western blots or immunoassays such as enzyme-linkedimmunosorbent assays (ELISA).

The disclosed methods relate generally to detection of multiple targetsin a single biological sample. In some embodiments, methods of detectingmultiple targets in a single biological sample using the same detectionchannel are disclosed. The targets may be present on the surface ofcells in suspension, on the surface of cytology smears, on the surfaceof histological sections, on the surface of DNA microarrays, on thesurface of protein microarrays, or on the surface of solid supports(such as gels, blots, glass slides, beads, or ELISA plates).

The methods disclosed herein may allow detection of a plurality oftargets in the same biological sample with little or no effect on theintegrity of the biological sample. Detecting the targets in the samebiological sample may further provide spatial information about thetargets in the biological sample. Methods disclosed herein may also beapplicable in analytical applications where a limited amount ofbiological sample may be available for analysis and the same sample mayhave to be processed for multiple analyses. Methods disclosed herein mayalso facilitate multiple analyses of solid-state samples (e.g., tissuesections) or samples adhered to a solid support (e.g., blots) withoutsubstantially stripping the probes and the targets. Furthermore, thesame detection channel may be employed for detection of differenttargets in the sample, enabling fewer chemistry requirements foranalyses of multiple targets. The methods may further facilitateanalyses based on detection methods that may be limited in the number ofsimultaneously detectable targets because of limitations of resolvablesignals. For example, using fluorescent-based detection, the number oftargets that may be simultaneously detected may be limited to about fouras only about four fluorescent signals may be resolvable based on theirexcitation and emission wavelength properties. In some embodiments, themethods disclosed herein may allow detection of greater than fourtargets using fluorescent-based detection system.

In some embodiments, the method is a high throughput multiplexingbiological sample analysis that includes a signal cycling process,wherein in each cycle, staining and imaging is followed by applying anelectron transfer reagent and irradiation of the biological sample. Themethod allows rapid signal cycling without significantly modifying thecomponents of the biological sample that are different from the probe.

In some embodiments, the method of detecting multiple targets in abiological sample includes sequential detection of targets in thebiological sample. The method generally includes the steps of detectinga first set of targets in the biological sample, bleaching the signalfrom the first set of targets by photoinduced chemical bleaching. Insome embodiments, the method further includes detecting a second set oftargets in the biological sample. The method may further includerepeating the step of photoinduced chemical bleaching of signal from thesecond set of targets, followed by detecting a third set of targets inthe biological sample, and so forth.

In some embodiments, the method includes the steps of contacting abiological sample with a first probe and physically binding a firstprobe to a first target. The method further includes observing a firstsignal from the first probe. An electron transfer reagent is applied tothe probe, and the sample containing the electron transfer reagent andthe probe is irradiated, thereby initiating a photoreaction thatmodifies the first signal. The method further includes contacting thebiological sample with a second probe and physically binding the secondprobe to a second target in the biological sample followed by observinga second signal from the second probe.

In some embodiments, the method also includes the steps of contacting abiological sample with a plurality of multiple sets of probes andphysically binding the plurality of probes to a plurality of targets.The method further includes observing a first set of signals from thefirst set of the plurality of probes. An electron transfer reagent isapplied to the plurality of probes, and the sample is irradiated,thereby initiating a photoreaction that modifies the first set ofsignals from the first set of the plurality of probes. The methodfurther includes generating the second set of signals from the secondset of the plurality of targets and observing the second set of signals.Generation of the second set of signals may comprise associating thesecond set of probes with a separate moiety that comprises signalgenerator. For example, the second set of probes may comprise a biotintag, and the moiety comprising signal generator may also comprisestreptavidin capable of binding the biotin tag. Alternatively,generation of the second set of signals may comprise un-masking thesignal-generating moiety, e.g., by modifying the distance between thefluorophore-quencher pair. In yet another embodiment, the second set ofsignals may arise from hybridization of labeled nucleic acid probes tounlabeled complementary sequences on the second set of probes.

In other embodiments, the method includes the steps of providing asample containing multiple targets and binding at least one probe havinga binder coupled to an enzyme to one or more target present in thesample. The method further includes reacting the bound probe with anenzyme substrate coupled to a signal generator and observing a signalfrom the signal generator. An electron transfer reagent thatsubstantially inactivates both the signal generator and the enzyme inthe course of a photoreaction is applied to the sample. The method alsoincludes an optional separate step of inactivating the enzyme. The stepof enzyme inactivation may comprise, e.g., application of an enzymeinactivation reagent. The method further includes binding at least onesubsequent probe having a binder coupled to an enzyme to one or moretarget present in the sample. The method further includes reacting thebound probe with an enzyme substrate coupled to a signal generator andobserving a signal from the signal generator.

In yet other embodiments, the method includes the steps of providing abiological sample containing multiple targets and binding at least oneprobe to one or more target present in the sample. The method furtherincludes observing a signal from the bound probe. The bound probe iscontacted with an electron transfer reagent, and the sample comprisingthe bound probe and the electron transfer reagent is irradiated, therebybleaching the probe. The method further includes binding at least onesubsequent probe to one or more target present in the sample followed byobserving a signal from the subsequent bound probe.

In yet other embodiments, the method includes the steps of providing abiological sample containing multiple targets and binding at least onefluorescent probe to one or more target present in the sample. Themethod further includes binding at least one control probe to one ormore target in the sample. The bound probe is contacted with an electrontransfer reagent, and the sample comprising the bound probe and theelectron transfer reagent is irradiated, thereby bleaching the probe andnot the control probe. The method further includes binding at least onesubsequent probe to one or more target present in the sample followed byobserving a signal from the subsequent bound probe.

In yet other embodiments, the methods described above provide a seriesof at least two images depicting optically labeled biological targets.

Biological Samples

A biological sample in accordance with one embodiment of the inventionmay be solid or fluid. Suitable examples of biological samples mayinclude, but are not limited to, cultures, blood, plasma, serum, saliva,cerebral spinal fluid, pleural fluid, milk, lymph, sputum, semen, urine,stool, tears, saliva, needle aspirates, external sections of the skin,respiratory, intestinal, and genitourinary tracts, tumors, organs, cellcultures or cell culture constituents, or solid tissue sections. Cellcultures may include mixed cell culture, stem cell colonies or culturesderived from various cancer or primary cell lines. In some embodiments,the biological sample may be analyzed as is, that is, without harvestand/or isolation of the target of interest. In an alternativeembodiment, harvesting and isolation of targets may be performed priorto analysis. In some embodiments, the methods disclosed herein may beparticularly suitable for in vitro analysis of biological samples.

A biological sample may include any of the aforementioned samplesregardless of their physical condition, such as, but not limited to,being frozen or stained or otherwise treated. In some embodiments, abiological sample may include compounds which are not naturallyintermixed with the sample in nature such as preservatives,anticoagulants, buffers, fixatives, nutrients, antibiotics, or the like.

In some embodiments, a biological sample may include a tissue sample orsection, a whole cell, a cell constituent, e.g., cell organelle, acytospin, or a cell smear. In some embodiments, a biological sampleessentially includes a tissue sample. A tissue sample may include acollection of similar cells obtained from a tissue of a biologicalsubject that may have a similar function. In some embodiments, a tissuesample may include a collection of similar cells obtained from a tissueof a human. Suitable examples of human tissues include, but are notlimited to, (1) epithelium; (2) the connective tissues, including bloodvessels, bone and cartilage; (3) muscle tissue; and (4) nerve tissue.The source of the tissue sample may be solid tissue obtained from afresh, frozen and/or preserved organ or tissue sample or biopsy oraspirate; blood or any blood constituents; bodily fluids such ascerebral spinal fluid, amniotic fluid, peritoneal fluid, or interstitialfluid; or cells from any time in gestation or development of thesubject. In some embodiments, the tissue sample may include primary orcultured cells or cell lines.

In some embodiments, a biological sample includes tissue sections fromhealthy or diseased tissue samples (e.g., tissue section from colon,breast tissue, prostate). A tissue section may include a single part orpiece of a tissue sample, for example, a thin slice of tissue or cellscut from a tissue sample. In some embodiments, multiple sections oftissue samples may be taken and subjected to analysis, provided themethods disclosed herein may be used for analysis of the same section ofthe tissue sample with respect to at least two different targets (atmorphological or molecular level). In some embodiments, tissuemicroarray may be used. In some embodiments, the same section of tissuesample may be analyzed with respect to at least four different targets(at morphological or molecular level). In some embodiments, the samesection of tissue sample may be analyzed with respect to greater thanfour different targets (at morphological or molecular level). In someembodiments, the same section of tissue sample may be analyzed at bothmorphological and molecular levels.

A tissue section, if employed as a biological sample may have athickness in a range that is less than about 100 micrometers, in a rangethat is less than about 50 micrometers, in a range that is less thanabout 25 micrometers, or in range that is less than about 10micrometers.

In some embodiments, the biological sample may comprise one or more ofproteins, carbohydrates or nucleic acids. In some embodiments, abiological sample or the targets in the biological sample may be adheredto a solid support. A solid support may include microarrays (e.g., DNAor RNA microarrays), gels, blots, glass slides, beads, or ELISA plates.In some embodiments, a biological sample or the targets in thebiological sample may be adhered to a membrane selected from nylon,nitrocellulose, and polyvinylidene difluoride. In some embodiments, thesolid support may include a plastic surface selected from polystyrene,polycarbonate, and polypropylene.

Targets

A target may be present on the surface of a biological sample (forexample, an antigen on a surface of a tissue section) or present in thebulk of the sample (for example, an antibody in a buffer solution). Insome embodiments, a target may not be inherently present on the surfaceof a biological sample and the biological sample may have to beprocessed to make the target available on the surface (e.g., antigenrecovery, enzymatic digestion, epitope retrieval, or blocking). In someembodiments, the target may be present in a body fluid such as blood,blood plasma, serum, or urine. In some other embodiments, the target maybe fixed in a tissue, either on a cell surface, or within a cell.

Suitability of targets to be analyzed may be determined by the type andnature of analysis required for the biological sample. In someembodiments, a target may provide information about the presence orabsence of an analyte in the biological sample. In another embodiment, atarget may provide information on a state of a biological sample. Forexample, if the biological sample includes a tissue sample, the methodsdisclosed herein may be used to detect targets that may help incomparing different types of cells or tissues, comparing differentdevelopmental stages, detecting the presence of a disease orabnormality, or determining the type of disease or abnormality.

Targets may include one or more of peptides, proteins (e.g., antibodies,affibodies, or aptamers), nucleic acids (e.g., polynucleotides, DNA,RNA, or aptamers); polysaccharides (e.g., lectins or sugars), lipids,enzymes, enzyme substrates, ligands, receptors, antigens, or haptens. Insome embodiments, targets may essentially include proteins or nucleicacids. In other embodiments, multiple types of targets, e.g., nucleicacids, polysaccharides, lipids, enzymes, enzyme substrates, ligands,receptors, antigens or haptens may be detected and/or analyzed in thesame biological sample in one or multiple cycles. One or more of theaforementioned targets may be characteristic of particular cells, whileother targets may be associated with a particular disease or condition.In some embodiments, targets that may be detected and analyzed using themethods disclosed herein may include, but are not limited to, prognostictargets, hormone or hormone receptor targets, lymphoid targets, tumortargets, cell cycle associated targets, neural tissue and tumor targets,or cluster differentiation targets.

Suitable examples of prognostic targets may include enzymatic targetssuch as galactosyl transferase II, neuron specific enolase, protonATPase-2, or acid phosphatase.

Suitable examples of hormone or hormone receptor targets may includehuman chorionic gonadotropin (HCG), adrenocorticotropic hormone,carcinoembryonic antigen (CEA), prostate-specific antigen (PSA),estrogen receptor, progesterone receptor, androgen receptor, gC1q-R/p33complement receptor, IL-2 receptor, p75 neurotrophin receptor, PTHreceptor, thyroid hormone receptor, or insulin receptor.

Suitable examples of lymphoid targets may includealpha-1-antichymotrypsin, alpha-1-antitrypsin, B cell target, bcl-2,bcl-6, B lymphocyte antigen 36 kD, BM1 (myeloid target), BM2 (myeloidtarget), galectin-3, granzyme B, HLA class I Antigen, HLA class II (DP)antigen, HLA class II (DQ) antigen, HLA class II (DR) antigen, humanneutrophil defensins, immunoglobulin A, immunoglobulin D, immunoglobulinG, immunoglobulin M, kappa light chain, kappa light chain, lambda lightchain, lymphocyte/histocyte antigen, macrophage target, muramidase(lysozyme), p80 anaplastic lymphoma kinase, plasma cell target,secretory leukocyte protease inhibitor, T cell antigen receptor (JOVI1), T cell antigen receptor (JOVI 3), terminal deoxynucleotidyltransferase, or unclustered B cell target.

Suitable examples of tumor targets may include alpha fetoprotein,apolipoprotein D, BAG-1 (RAP46 protein), CA19-9 (sialyl lewisa), CA50(carcinoma associated mucin antigen), CA125 (ovarian cancer antigen),CA242 (tumour associated mucin antigen), chromogranin A, clusterin(apolipoprotein J), epithelial membrane antigen, epithelial-relatedantigen, epithelial specific antigen, gross cystic disease fluidprotein-15, hepatocyte specific antigen, heregulin, human gastric mucin,human milk fat globule, MAGE-1, matrix metalloproteinases, melan A,melanoma target (HMB45), mesothelin, metallothionein, microphthalmiatranscription factor (MITF), Muc-1 core glycoprotein. Muc-1glycoprotein, Muc-2 glycoprotein, Muc-5AC glycoprotein, Muc-6glycoprotein, myeloperoxidase, Myf-3 (Rhabdomyosarcoma target), Myf-4(Rhabdomyosarcoma target), MyoD1 (Rhabdomyosarcoma target), myoglobin,nm23 protein, placental alkaline phosphatase, prealbumin, prostatespecific antigen, prostatic acid phosphatase, prostatic inhibin peptide,PTEN, renal cell carcinoma target, small intestinal mucinous antigen,tetranectin, thyroid transcription factor-1, tissue inhibitor of matrixmetalloproteinase 1, tissue inhibitor of matrix metalloproteinase 2,tyrosinase, tyrosinase-related protein-1, villin, or von Willebrandfactor.

Suitable examples of cell cycle associated targets may include apoptosisprotease activating factor-1, bcl-w, bcl-x, bromodeoxyuridine, CAK(cdk-activating kinase), cellular apoptosis susceptibility protein(CAS), caspase 2, caspase 8, CPP32 (caspase-3), CPP32 (caspase-3),cyclin dependent kinases, cyclin A, cyclin B1, cyclin D1, cyclin D2,cyclin D3, cyclin E, cyclin G, DNA fragmentation factor (N-terminus),Fas (CD95), Fas-associated death domain protein, Fas ligand, Fen-1,IPO-38, Mcl-1, minichromosome maintenance proteins, mismatch repairprotein (MSH2), poly (ADP-Ribose) polymerase, proliferating cell nuclearantigen, p16 protein, p27 protein, p34cdc2, p57 protein (Kip2), p105protein, Stat 1 alpha, topoisomerase I, topoisomerase II alpha,topoisomerase III alpha, or topoisomerase II beta.

Suitable examples of neural tissue and tumor targets may include alpha Bcrystallin, alpha-internexin, alpha synuclein, amyloid precursorprotein, beta amyloid, calbindin, choline acetyltransferase, excitatoryamino acid transporter 1, GAP43, glial fibrillary acidic protein,glutamate receptor 2, myelin basic protein, nerve growth factor receptor(gp75), neuroblastoma target, neurofilament 68 kD, neurofilament 160 kD,neurofilament 200 kD, neuron specific enolase, nicotinic acetylcholinereceptor alpha4, nicotinic acetylcholine receptor beta2, peripherin,protein gene product 9, S-100 protein, serotonin, SNAP-25, synapsin I,synaptophysin, tau, tryptophan hydroxylase, tyrosine hydroxylase, orubiquitin.

Suitable examples of cluster differentiation targets may include CD1a,CD1b, CD1c, CD1d, CD1e, CD2, CD3delta, CD3epsilon, CD3gamma, CD4, CD5,CD6, CD7, CD8alpha, CD8beta, CD9, CD10, CD11a, CD11b, CD11c, CDw12,CD13, CD14, CD15, CD15s, CD16a, CD16b, CDw17, CD18, CD19, CD20, CD21,CD22, CD23, CD24, CD25, CD26, CD27, CD28, CD29, CD30, CD31, CD32, CD33,CD34, CD35, CD36, CD37, CD38, CD39, CD40, CD41, CD42a, CD42b, CD42c,CD42d, CD43, CD44, CD44R, CD45, CD46, CD47, CD48, CD49a, CD49b, CD49c,CD49d, CD49e, CD49f, CD50, CD51, CD52, CD53, CD54, CD55, CD56, CD57,CD58, CD59, CDw60, CD61, CD62E, CD62L, CD62P, CD63, CD64, CD65, CD65s,CD66a, CD66b, CD66c, CD66d, CD66e, CD66f, CD68, CD69, CD70, CD71, CD72,CD73, CD74, CDw75, CDw76, CD77, CD79a, CD79b, CD80, CD81, CD82, CD83,CD84, CD85, CD86, CD87, CD88, CD89, CD90, CD91, CDw92, CDw93, CD94,CD95, CD96, CD97, CD98, CD99, CD100, CD101, CD102, CD103, CD104, CD105,CD106, CD107a, CD107b, CDw108, CD109, CD114, CD115, CD116, CD117,CDw119, CD120a, CD120b, CD121a, CDw121b, CD122, CD123, CD124, CDw125,CD126, CD127, CDw128a, CDw128b, CD130, CDw131, CD132, CD134, CD135,CDw136, CDw137, CD138, CD139, CD140a, CD140b, CD141, CD142, CD143,CD144, CDw145, CD146, CD147, CD148, CDw149, CDw150, CD151, CD152, CD153,CD154, CD155, CD156, CD157, CD158a, CD158b, CD161, CD162, CD163, CD164,CD165, CD166, and TCR-zeta.

Other suitable prognostic targets may include centromere protein-F(CENP-F), giantin, involucrin, lamin A&C (XB 10), LAP-70, mucin, nuclearpore complex proteins, p180 lamellar body protein, ran, r, cathepsin D,Ps2 protein, Her2-neu, P53, S100, epithelial target antigen (EMA), TdT,MB2, MB3, PCNA, or Ki67.

Probes

In some embodiments, a binder and a label (signal generator or anenzyme) may be coupled to each other directly (that is without anylinkers). In other embodiments, a binder and a label (signal generatoror an enzyme) may be coupled to each other via a linker. As used herein,“coupled” generally refers to two entities (for example, binder andsignal generator) stably bound to one another by any physicochemicalmeans. The nature of the coupling may be such that it does notsubstantially impair the effectiveness of either entity. A binder and alabel may be coupled to each other through covalent or non-covalentinteractions. Non-covalent interactions may include, but are not limitedto, hydrophobic interactions, ionic interactions, hydrogen-bondinteractions, high affinity interactions (such as, biotin-avidin orbiotin-streptavidin complexation), or other affinity interactions.

In some embodiments, a binder and a label (signal generator or anenzyme) may be chemically linked to each other through functional groupscapable of reacting and forming a linkage under suitable conditions.Suitable examples of functional group combinations may include, but arenot limited to, amine ester and amines or anilines; acyl azide andamines or anilines; acyl halides and amines, anilines, alcohols, orphenols; acyl nitrile and alcohols or phenols; aldehyde and amines oranilines; alkyl halide and amines, anilines, alcohols, phenols orthiols; alkyl sulfonate and thiols, alcohols or phenols; anhydride andalcohols, phenols, amines or anilines; aryl halide and thiols; aziridineand thiols or thioethers; carboxylic acid and amines, anilines, alcoholsor alkyl halides; diazoalkane and carboxylic acids; epoxide and thiols;haloacetamide and thiols; halotriazin and amines, anilines or phenols;hydrazine and aldehydes or ketones; hydroxyamine and aldehydes orketones; imido ester and amines or anilines; isocyanate and amines oranilines; and isothiocyanate and amines or anilines. A functional groupin one of the aforementioned functional group pair may be present in abinder and a corresponding functional group may be present in the signalgenerator or the enzyme. For example, a binder may include a carboxylicacid and the signal generator or the enzyme may include an amine,aniline, alcohol or acyl halide, or vice versa. Conjugation between thebinder and the signal generator or the enzyme may be effected in thiscase by formation of an amide or an ester linkage.

In some embodiments, the binder may be intrinsically labeled with asignal generator (for example, if the binder is a protein, duringsynthesis using a detectably labeled amino acid) or an enzyme (forexample, if the binder is an enzyme). A binder that is intrinsicallylabeled may not require a separate signal generator or an enzyme inorder to be detected. Rather the intrinsic label may be sufficient forrendering the probe detectable. In alternate embodiments, the binder maybe labeled by binding to it a specific signal generator or an enzyme(i.e., extrinsically labeled).

In some embodiments, the binder and the label (signal generator or theenzyme) are embodied in a single entity. In alternative embodiments, thebinder and the label (signal generator or the enzyme) are embodied indiscrete entities (e.g., a primary antibody capable of binding a targetand an enzyme or a signal generator-labeled secondary antibody capableof binding the primary antibody or a hapten labeled primary antibodycapable of binding a target and an enzyme or a signal generator-labeledanti-hapten antibody capable of binding the hapten labeled primaryantibody). When the binder and the signal generator or the enzyme areseparate entities they may be applied to a biological sample in a singlestep or multiple steps. In some embodiments, the binder and the label(signal generator or the enzyme) are separate entities that arepre-attached before application to the biological sample and applied tothe biological sample in a single step. In yet other embodiments, thebinder and the label (signal generator or the enzyme) are separateentities that are applied to the biological sample independently andcombine following application.

Binders

The methods disclosed herein involve the use of binders that physicallybind to the target in a specific manner. In some embodiments, a bindermay bind to a target with sufficient specificity, that is, a binder maybind to a target with greater affinity than it does to any othermolecule. In some embodiments, the binder may bind to other molecules,but the binding may be such that the non-specific binding may be at ornear background levels. In some embodiments, the affinity of the binderfor the target of interest may be in a range that is at least 2-fold, atleast 5-fold, at least 10-fold, or more than its affinity for othermolecules. In some embodiments, binders with the greatest differentialaffinity may be employed, although they may not be those with thegreatest affinity for the target.

In some embodiments, binding between the target and the binder may beaffected by physical binding. Physical binding may include bindingeffected using non-covalent interactions. Non-covalent interactions mayinclude, but are not limited to, hydrophobic interactions, ionicinteractions, hydrogen-bond interactions, or affinity interactions (suchas, biotin-avidin or biotin-streptavidin complexation). In someembodiments, the target and the binder may have areas on their surfacesor in cavities giving rise to specific recognition between the tworesulting in physical binding. In some embodiments, a binder may bind toa biological target based on the reciprocal fit of a portion of theirmolecular shapes.

Binders and their corresponding targets may be considered as bindingpairs, of which non-limiting examples include immune-type binding-pairs,such as, antigen/antibody, antigen/antibody fragment, orhapten/anti-hapten; nonimmune-type binding-pairs, such as biotin/avidin,biotin/streptavidin, folic acid/folate binding protein, hormone/hormonereceptor, lectin/specific carbohydrate, enzyme/enzyme, enzyme/substrate,enzyme/substrate analog, enzyme/pseudo-substrate (substrate analogs thatcannot be catalyzed by the enzymatic activity), enzyme/co-factor,enzyme/modulator, enzyme/inhibitor, or vitamin B12/intrinsic factor.Other suitable examples of binding pairs may include complementarynucleic acid fragments (including DNA sequences, RNA sequences, LNAsequences, and PNA sequences or other modified nucleic acids known inthe literature); Protein A/antibody; Protein G/antibody; nucleicacid/nucleic acid binding protein; or polynucleotide/polynucleotidebinding protein.

In some embodiments, the binder may be a sequence- or structure-specificbinder, wherein the sequence or structure of a target recognized andbound by the binder may be sufficiently unique to that target.

In some embodiments, the binder may be structure-specific and mayrecognize a primary, secondary, or tertiary structure of a target. Aprimary structure of a target may include specification of its atomiccomposition and the chemical bonds connecting those atoms (includingstereochemistry), for example, the type and nature of linear arrangementof amino acids in a protein. A secondary structure of a target may referto the general three-dimensional form of segments of biomolecules, forexample, for a protein a secondary structure may refer to the folding ofthe peptide “backbone” chain into various conformations that may resultin distant amino acids being brought into proximity with each other.Suitable examples of secondary structures may include, but are notlimited to, alpha helices, beta pleated sheets, or random coils. Atertiary structure of a target may be is its overall three dimensionalstructure. A quaternary structure of a target may be the structureformed by its noncovalent interaction with one or more other targets ormacromolecules (such as protein interactions). An example of aquaternary structure may be the structure formed by the four-globinprotein subunits to make hemoglobin. A binder in accordance with theembodiments of the invention may be specific for any of theafore-mentioned structures.

An example of a structure-specific binder may include a protein-specificmolecule that may bind to a protein target. Examples of suitableprotein-specific molecules may include antibodies and antibodyfragments, nucleic acids (for example, aptamers that recognize proteintargets), or protein substrates (non-catalyzable).

In some embodiments, a target may include an antigen and a binder mayinclude an antibody. A suitable antibody may include monoclonalantibodies, polyclonal antibodies, multispecific antibodies (forexample, bispecific antibodies), or antibody fragments so long as theybind specifically to a target antigen.

In some embodiments, a biological sample may include a cell or a tissuesample and the methods disclosed herein may be employed inimmunohistochemistry (IHC). Immunochemistry may involve binding of atarget antigen to an antibody-based binder to provide information aboutthe tissues or cells (for example, diseased versus normal cells).Examples of antibodies (and the corresponding diseases/disease cells)suitable as binders for methods disclosed herein include, but are notlimited to, anti-estrogen receptor antibody (breast cancer),anti-progesterone receptor antibody (breast cancer), anti-p53 antibody(multiple cancers), anti-Her-2/neu antibody (multiple cancers),anti-EGFR antibody (epidermal growth factor, multiple cancers),anti-cathepsin D antibody (breast and other cancers), anti-Bcl-2antibody (apoptotic cells), anti-E-cadherin antibody, anti-CA125antibody (ovarian and other cancers), anti-CA15-3 antibody (breastcancer), anti-CA19-9 antibody (colon cancer), anti-c-erbB-2 antibody,anti-P-glycoprotein antibody (MDR, multi-drug resistance), anti-CEAantibody (carcinoembryonic antigen), anti-retinoblastoma protein (Rb)antibody, anti-ras oneoprotein (p21) antibody, anti-Lewis X (also calledCD15) antibody, anti-Ki-67 antibody (cellular proliferation), anti-PCNA(multiple cancers) antibody, anti-CD 3 antibody (T-cells), anti-CD4antibody (helper T cells), anti-CD5 antibody (T cells), anti-CD7antibody (thymocytes, immature T cells, NK killer cells), anti-CD8antibody (suppressor T cells), anti-CD9/p24 antibody (ALL), anti-CD10(also called CALLA) antibody (common acute lymphoblastic leukemia),anti-CD11c antibody (Monocytes, granulocytes, AML), anti-CD13 antibody(myelomonocytic cells, AML), anti-CD14 antibody (mature monocytes,granulocytes), anti-CD15 antibody (Hodgkin's disease), anti-CD19antibody (B cells), anti-CD20 antibody (B cells), anti-CD22 antibody (Bcells), anti-CD 23 antibody (activated B cells, CLL), anti-CD30 antibody(activated T and B cells, Hodgkin's disease), anti-CD31 antibody(angiogenesis marker), anti-CD33 antibody (myeloid cells, AML),anti-CD34 antibody (endothelial stem cells, stromal tumors), anti-CD35antibody (dendritic cells), anti-CD38 antibody (plasma cells, activatedT, B, and myeloid cells), anti-CD 41 antibody (platelets,megakaryocytes), anti-LCA/CD45 antibody (leukocyte common antigen),anti-CD45RO antibody (helper, inducer T cells), anti-CD45RA antibody (Bcells), anti-CD39, CD100 antibody, anti-CD95/Fas antibody (apoptosis),anti-CD99 antibody (Ewings Sarcoma marker, MIC2 gene product),anti-CD106 antibody (VCAM-1; activated endothelial cells),anti-ubiquitin antibody (Alzheimer's disease), anti-CD71 (transferrinreceptor) antibody, anti-c-myc (oncoprotein and a hapten) antibody,anti-cytokeratins (transferrin receptor) antibody, anti-vimentins(endothelial cells) antibody (B and T cells), anti-HPV proteins (humanpapillomavirus) antibody, anti-kappa light chains antibody (B cell),anti-lambda light chains antibody (B cell), anti-melanosomes (HMB45)antibody (melanoma), anti-prostate specific antigen (PSA) antibody(prostate cancer), anti-S-100 antibody (melanoma, salivary, glialcells), anti-tau antigen antibody (Alzheimer's disease), anti-fibrinantibody (epithelial cells), anti-keratins antibody, anti-cytokeratinantibody (tumor), anti-alpha-catenin (cell membrane), or anti-Tn-antigenantibody (colon carcinoma, adenocarcinomas, and pancreatic cancer).

Other specific examples of suitable antibodies may include, but are notlimited to, anti proliferating cell nuclear antigen, clone pc10 (SigmaAldrich, P8825); anti smooth muscle alpha actin (5 mA), clone 1A4(Sigma, A2547); rabbit anti beta catenin (Sigma, C 2206); mouse anti pancytokeratin, clone PCK-26 (Sigma, C1801); mouse anti estrogen receptoralpha, clone 1D5 (DAKO, M 7047); beta catenin antibody, clone 15B8(Sigma, C 7738); goat anti vimentin (Sigma, V4630); cycle androgenreceptor clone AR441 (DAKO, M3562); Von Willebrand Factor 7, keratin 5,keratin 8/18, e-cadherin, Her2/neu, Estrogen receptor, p53, progesteronereceptor, beta catenin; donkey anti-mouse (Jackson Immunoresearch,715-166-150); or donkey anti rabbit (Jackson Immunoresearch,711-166-152).

In some embodiments, a binder may be sequence-specific. Asequence-specific binder may include a nucleic acid and the binder maybe capable of recognizing a particular linear arrangement of nucleotidesor derivatives thereof in the target. In some embodiments, the lineararrangement may include contiguous nucleotides or derivatives thereofthat may each bind to a corresponding complementary nucleotide in thebinder. In an alternate embodiment, the sequence may not be contiguousas there may be one, two, or more nucleotides that may not havecorresponding complementary residues on the probe. Suitable examples ofnucleic acid-based binders may include, but are not limited to, DNA orRNA oligonucleotides or polynucleotides. In some embodiments, suitablenucleic acids may include nucleic acid analogs, such as dioxygenin dCTP,biotin dcTP 7-azaguanosine, azidothymidine, inosine, or uridine.

In certain embodiments, both the binder and the target may includenucleic acids. In some embodiments, a nucleic-acid based binder may forma Watson-Crick bond with the nucleic acid target. In another embodiment,the nucleic acid binder may form a Hoogsteen bond with the nucleic acidtarget, thereby forming a triplex. A nucleic acid binder that binds byHoogsteen binding may enter the major groove of a nucleic acid targetand hybridizes with the bases located there. Suitable examples of theabove binders may include molecules that recognize and bind to the minorand major grooves of nucleic acids (for example, some forms ofantibiotics.) In certain embodiments, the nucleic acid binders may formboth Watson-Crick and Hoogsteen bonds with the nucleic acid target (forexample, bis PNA probes are capable of both Watson-Crick and Hoogsteenbinding to a nucleic acid).

The length of nucleic acid binder may also determine the specificity ofbinding. The energetic cost of a single mismatch between the binder andthe nucleic acid target may be relatively higher for shorter sequencesthan for longer ones. In some embodiments, hybridization of smallernucleic acid binders may be more specific than the hybridization oflonger nucleic acid probes, as the longer probes may be more amenable tomismatches and may continue to bind to the nucleic acid depending on theconditions. In certain embodiments, shorter binders may exhibit lowerbinding stability at a given temperature and salt concentration. Bindersthat may exhibit greater stability to bind short sequences may beemployed in this case (for examples, bis PNA). In some embodiments, thenucleic acid binder may have a length in range of from about 4nucleotides to about 12 nucleotides, from about 12 nucleotides to about25 nucleotides, from about 25 nucleotides to about 50 nucleotides, fromabout 50 nucleotides to about 100 nucleotides, from about 100nucleotides to about 250 nucleotides, from about 250 nucleotides toabout 500 nucleotides, or from about 500 nucleotides to about 1000nucleotides. In some embodiments, the nucleic acid binder may have alength in a range that is greater than about 1000 nucleotides.Notwithstanding the length of the nucleic acid binder, all thenucleotide residues of the binder may not hybridize to complementarynucleotides in the nucleic acid target. For example, the binder mayinclude 50 nucleotide residues in length, and only 25 of thosenucleotide residues may hybridize to the nucleic acid target. In someembodiments, the nucleotide residues that may hybridize may becontiguous with each other. The nucleic acid binders may be singlestranded or may include a secondary structure. In some embodiments, abiological sample may include a cell or a tissue sample and thebiological sample may be subjected to in-situ hybridization (ISH) usinga nucleic acid binder. In some embodiments, a tissue sample may besubjected to in situ hybridization in addition to immunohistochemistry(IHC) to obtain desired information from the sample.

Regardless of the type of binder and the target, the specificity ofbinding between the binder and the target may also be affected dependingon the binding conditions (for example, hybridization conditions in caseof complementary nucleic acids). Suitable binding conditions may berealized by modulation one or more of pH, temperature, or saltconcentration.

A binder may be intrinsically labeled (signal generator or enzymeattached during synthesis of binder) or extrinsically labeled (signalgenerator or enzyme attached during a later step). For example for aprotein-based binder, an intrinsically labeled binder may be prepared byemploying labeled amino acids. Similarly, an intrinsically labelednucleic acid may be synthesized using methods that incorporate signalgenerator-labeled nucleotides or signal generator labeled nucleosidephosphoramidites directly into the growing nucleic acid depending uponthe method used for nucleic acid synthesis. In some embodiments, abinder may be synthesized in a manner such that signal generators orenzymes may be incorporated at a later stage. For example, this latterlabeling may be accomplished by chemical means by the introduction ofactive amino or thiol groups into nucleic acids or peptide chains. Insome embodiments, a binder such as a protein (for example, an antibody)or a nucleic acid (for example, a DNA) may be directly chemicallylabeled using appropriate chemistries.

In some embodiments, combinations of binders may be used that mayprovide greater specificity or in certain embodiments amplification ofthe signal. Thus, in some embodiments, a sandwich of binders may beused, where the first binder may bind to the target and serve to providefor secondary binding, where the secondary binder may or may not includea label, which may further provide for tertiary binding (if required)where the tertiary binding member may include a label.

Suitable examples of binder combinations may include primaryantibody-secondary antibody, complementary nucleic acids, or otherligand-receptor pairs (such as biotin-streptavidin). Some specificexamples of suitable binder pairs may include mouse anti-myc forrecombinant expressed proteins with c-myc epitope; mouse anti-HisG forrecombinant protein with His-Tag epitope, mouse anti-express forrecombinant protein with epitope-tag, rabbit anti-goat for goat IgGprimary molecules, complementary nucleic acid sequence for a nucleicacid; mouse anti-thio for thioredoxin fusion proteins, rabbit anti-GFPfor fusion protein, jacalin for .alpha.-D-galactose; and melibiose forcarbohydrate-binding proteins, sugars, nickel couple matrix or heparin.

In some embodiments, a combination of a primary antibody and a secondaryantibody may be used as a binder. A primary antibody may be capable ofbinding to a specific region of the target and the secondary antibodymay be capable of binding to the primary antibody. A secondary antibodymay be attached to a signal generator or an enzyme before binding to theprimary antibody or may be capable of binding to a signal generator oran enzyme at a later step. In an alternate embodiment, a primaryantibody and specific binding ligand-receptor pairs (such asbiotin-streptavidin) may be used. The primary antibody may be attachedto one member of the pair (for example biotin) and the other member (forexample streptavidin) may be labeled with a signal generator or anenzyme. The secondary antibody, avidin, streptavidin, or biotin may beeach independently labeled with a signal generator or an enzyme.

In some embodiments, the methods disclosed herein may be employed in animmunostaining procedure, and a primary antibody may be used tospecifically bind the target protein. A secondary antibody may be usedto specifically bind to the primary antibody, thereby forming a bridgebetween the primary antibody and a subsequent reagent (for example asignal generator or enzyme), if any. For example, a primary antibody maybe mouse IgG (an antibody created in mouse) and the correspondingsecondary antibody may be goat anti-mouse (antibody created in goat)having regions capable of binding to a region in mouse IgG.

In some embodiments, signal amplification may be obtained when severalsecondary antibodies may bind to epitopes on the primary antibody. In animmunostaining procedure a primary antibody may be the first antibodyused in the procedure and the secondary antibody may be the secondantibody used in the procedure. In other embodiments a third antibodymay be used to further increase signal. For example, an antibody raisedin mouse may be used to bind the target. A goat-anti-mouse secondaryantibody may be used to bind the primary antibody and a labeleddonkey-anti-goat antibody may be used as a tertiary antibody to bind tothe secondary antibodies already bound to the primary antibody whichitself is bound to the target. In some embodiments, a primary antibodymay be the only antibody used in an immunostaining procedure.

Signal Generators

The type of signal generator suitable for the methods disclosed hereinmay depend on a variety of factors, including the nature of the analysisbeing conducted, the type of the energy source and detector used, thetype of electron transfer reagent employed, the type of binder, the typeof target.

A suitable signal generator may include a molecule or a compound capableof providing a detectable signal. A signal generator may provide acharacteristic signal following interaction with an energy source or acurrent. An energy source may include electromagnetic radiation sourceand a fluorescence excitation source. Electromagnetic radiation sourcemay be capable of providing electromagnetic energy of any wavelengthincluding visible, infrared and ultraviolet. Electromagnetic radiationmay be in the form of a direct light source or may be emitted by a lightemissive compound such as a donor fluorophore. A fluorescence excitationsource may be capable of making a source fluoresce or may give rise tophotonic emissions (that is, electromagnetic radiation, directedelectric field, temperature, physical contact, or mechanicaldisruption). Suitable signal generators may provide a signal capable ofbeing detected by a variety of methods including optical measurements(for example, fluorescence), electrical conductivity, or radioactivity.Suitable signal generators may be, for example, light emitting, energyaccepting, fluorescing, radioactive, or quenching.

A suitable signal generator may be sterically and chemically compatiblewith the constituents to which it is bound, for example, a binder.Additionally, a suitable signal generator may not interfere with thebinding of the binder to the target, nor may it significantly affect thebinding specificity of the binder. A suitable signal generator may beorganic or inorganic in nature. In some embodiments, a signal generatormay be of a chemical, peptide or nucleic acid nature.

A suitable signal generator may be directly detectable. A directlydetectable moiety may be one that may be detected directly by itsability to emit a signal, such as for example a fluorescent label thatemits light of a particular wavelength following excitation by light ofanother lower, characteristic wavelength and/or absorb light of aparticular wavelength.

A signal generator, suitable in accordance with the methods disclosedherein may be amenable to manipulation on application of an electrontransfer reagent. In some embodiments, a signal generator may be capableof being bleached, e.g., the signal it generates may be diminished ordestroyed as result of the signal generator being modified in the courseof a photoreaction. Chemical modification may include completedisintegration of the signal generator or modification of thesignal-generating component of the signal generator. In someembodiments, the signal generator is charged.

Modification of the signal-generating component may include any chemicalmodification (such as addition, substitution, or removal) that mayresult in the modification of the signal generating properties. Forexample, unconjugating a conjugated signal generator may result indestruction of chromogenic properties of the signal generator.Similarly, substitution of a fluorescence-inhibiting functional group ona fluorescent signal generator may result in modification of itsfluorescent properties. In some embodiments, one or more signalgenerators substantially resistant to inactivation by a specificchemical agent may be used as a control probe in the provided methods.

In some embodiments, a signal generator may be selected from a lightemissive molecule, a radioisotope (e.g., P³² or H³, ¹⁴C, ¹²⁵I and ¹³¹I)an optical or electron density marker, a Raman-active tag, an electronspin resonance molecule (such as for example nitroxyl radicals), anelectrical charge transferring molecule (i.e., an electrical chargetransducing molecule), a semiconductor nanocrystal, a semiconductornanoparticle, a colloid gold nanocrystal, a microbead, a magnetic bead,a paramagnetic particle.

In some embodiments, a signal generator may be an optical signalgenerator, e.g., may include a light-emissive molecule. A light emissivemolecule may emit light in response to irradiation with light of aparticular wavelength. Light emissive molecules may be capable ofabsorbing and emitting light through luminescence (non-thermal emissionof electromagnetic radiation by a material upon excitation),phosphorescence (delayed luminescence as a result of the absorption ofradiation), chemiluminescence (luminescence due to a chemical reaction),fluorescence, or polarized fluorescence. Non-limiting examples ofoptical signal generators include a fluorescent signal generator, e.g.,a fluorophore, a Raman-active tag or a chromophore.

In some embodiments, a signal generator may essentially include afluorophore. In some embodiments, a signal generator may essentiallyinclude a fluorophore attached to an antibody, for example, in animmunohistochemistry analysis. Suitable fluorophores that may beconjugated to a primary antibody include, but are not limited to,Fluorescein, Rhodamine, Texas Red, VECTOR Red, ELF (Enzyme-LabeledFluorescence), Cy2, Cy3, Cy3.5, Cy5, Cy7, Fluor X, Calcein, Calcein-AM,CRYPTOFLUOR, Orange (42 kDa), Tangerine (35 kDa), Gold (31 kDa), Red (42kDa), Crimson (40 kDa), BHMP, BHDMAP, Br-Oregon, Lucifer Yellow, Alexadye family, N-[6-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)amino]caproyl](NBD), BODIPY, boron dipyrromethene difluoride,1,3-dichloro-7-hydroxy-9,9-dimethyl-2(9H)-Acridinone (DDAO),dimethylacridinone (DAO), Oregon Green, MITOTRACKER Red, Phycoerythrin,Phycobiliproteins BPE (240 kDa) RPE (240 kDa) CPC (264 kDa) APC (104kDa), Spectrum Blue, Spectrum Aqua, Spectrum Green, Spectrum Gold,Spectrum Orange, Spectrum Red, Infra-Red (IR) Dyes, Cyclic GDP-Ribose(cGDPR), Calcofluor White, Lissamine, Umbelliferone, Tyrosine orTryptophan. In some embodiments, the fluorophore can be cyanine,rhodamine, coumarins or pyrelium dyes. In some embodiments, a signalgenerator may essentially include a cyanine dye. In further embodiments,a signal generator may essentially include one or more a Cy2 dye, a Cy3dye, a Cy5 dye, or a Cy7 dye. In alternative embodiments, the signalgenerator may be BODIPY, rhodamine,1,3-dichloro-7-hydroxy-9,9-dimethyl-2(9H)-Acridinone (DDAO) or7-hydroxy-9,9-dimethyl-2(9H)-Acridinone (DAO).

In some embodiments, the signal generator may be part of a FRET pair.FRET pair includes two fluorophores that are capable of undergoing FRETto produce or eliminate a detectable signal when positioned in proximityto one another. Some examples of donors may include Alexa 488, Alexa546, BODIPY 493, Oyster 556, Fluor (FAM), Cy3, or TTR (Tamra). Someexamples of acceptors may include Cy5, Alexa 594, Alexa 647, or Oyster656.

As described hereinabove, one or more of the aforementioned moleculesmay be used as a signal generator. In some embodiments, one or more ofthe signal generators may be amenable to signal destruction and thesignal generator may essentially include a molecule capable of beingbleached by photoactivated chemical bleaching. In some embodiments, asignal generator may include a fluorophore capable of being chemicallymodified in a photoreaction that also involves an electron transferreagent and irradiation. In some embodiments, a signal generator mayessentially include cyanine, BODIPY, rhodamine, or acridinone (e.g.,DDAO and DAO), that can be modified in a photoreaction that alsoinvolves addition of an electron transfer reagent and irradiation. Insome embodiments, a signal generator may include one or more a Cy2 dye,a Cy3 dye, a Cy5 dye, or a Cy7 dye that can be bleached byphotoactivated chemical bleaching.

Enzyme and Enzyme Substrates

In some embodiments, a probe may include a binder coupled to an enzyme.In some embodiments, a suitable enzyme catalyzes a chemical reaction ofthe substrate to form a reaction product that can bind to a receptor(e.g., phenolic groups) present in the sample. A receptor may beexogeneous (that is, a receptor extrinsically adhered to the sample orthe solid-support) or endogeneous (receptors present intrinsically inthe sample or the solid-support). Signal amplification may be effectedas a single enzyme may catalyze a chemical reaction of the substrate tocovalently bind multiple signal generators near the target.

In some embodiments, a suitable enzyme may also be capable of beinginactivated in the course of a photoreaction. Examples of suitableenzymes include peroxidases, oxidases, phosphatases, esterases, andglycosidases. Specific examples of suitable enzymes include horseradishperoxidase, alkaline phosphatase, β-D-galactosidase, lipase, and glucoseoxidase. In some embodiments, the enzyme is a peroxidase selected fromhorseradish peroxidase, cytochrome C peroxidase, glutathione peroxidase,microperoxidase, myeloperoxidase, lactoperoxidase, and soybeanperoxidase.

In some embodiments, an enzyme is not inactivated in the course of aphotoreaction, but is inactivated in a separate inactivation stepcarried out before or after the photoreaction is completed. Theinactivation step may include application of an enzyme inactivationreagent to the sample containing the enzyme.

In some embodiments, a binder and an enzyme may be embodied in a singleentity, for example a protein molecule capable of binding to a targetand also catalyzing a chemical reaction of substrate. In otherembodiments, a binder and an enzyme may be embodied in separate entitiesand may be coupled by covalent bond formation or by usingligand-receptor conjugate pairs (e.g., biotin streptavidin).

An enzyme substrate may be selected depending on the enzyme employed andthe target available for binding in the sample. For example, inembodiments including HRP as an enzyme, a substrate may include asubstituted phenol (e.g., tyramine). Reaction of HRP to the tyramine mayproduce an activated phenolic substrate that may bind to endogeneousreceptors like electron-rich moieties (such as tyrosine or tryptophan)or phenolic groups present in the surface proteins of a biologicalsample. In alternate embodiments, where 3-methyl-2-benzothiazolinonehydrochloride (MBTH) may be employed as a substrate along with an HRPenzyme, exogeneous receptors like p-dimethylaminobenzaldehyde (DMAB) maybe adhered to the solid support or the biological sample before reactingwith the substrate.

In some embodiments, an enzyme substrate may be dephosphorylated afterreaction with the enzyme. The dephosphorylated reaction product may becapable of binding to endogeneous or exogeneous receptors (e.g.,antibodies) in the sample or the solid-support. For example, an enzymemay include alkaline phosphatase (AP) and a substrate may include NADP,substituted phosphates (e.g., nitrophenyl phosphate), or phosphorylatedbiotin. The receptors may include NAD binding proteins, antibodies tothe dephosphorylated reaction product (e.g., anti nitro-phenol), avidin,or streptavidin accordingly. In some embodiments, a substrate mayproduce insoluble product upon action of the enzyme which may deposit invicinity of where they are generated. Non-limiting examples of suchsubstrates may include diaminobenzidine (DAB) for HRP and ELF for AP.

In some embodiments, an enzyme may include β-galactosidase and asubstrate may include β-galactopyranosyl-glycoside of fluorescein orcoumarin. Receptors may include antibodies to deglycosylated moieties(e.g., anti-fluorescein or anti-coumarin). In some embodiments, multipleenzyme combinations like HRP/AP may be used as an enzyme. A substratemay include phosphorylated substituted phenol e.g., tyrosine phosphate,which may be dephosphorylated by AP before reacting with HRP to form areaction product capable of binding to phenolic groups or electron richmoieties-based receptors.

A reaction product of the enzyme substrate may further be capable ofproviding a detectable signal. In some embodiments, enzyme substratesemployed in the methods disclosed herein may include non-chromogenic ornon-chemiluminescent substrates, that is a reaction of the enzyme andthe enzyme substrate may not itself produce a detectable signal. Enzymesubstrates employed in the methods disclosed herein may include anextrinsic signal generator (e.g., a fluorophore) as a label. The signalgenerator and the enzyme substrate may be attached directly (e.g., anenzyme substrate with a fluorescent label) or indirectly (e.g., throughligand-receptor conjugate pair). In some embodiments, a substrate mayinclude protected functional groups (e.g., sulfhydryl groups). Afterbinding of the activated substrate to the receptors, the functionalgroup may be deprotected and conjugation to a signal generator effectedusing a signal generator having a thiol reactive group (e.g., maleimideor iodoacetyl).

In some embodiments, a probe may include horseradish peroxidase and thesubstrate is selected from substituted phenols (e.g., tyramine). In someembodiments, the horseradish peroxidase causes the activated phenolicsubstrate to covalently bind to phenolic groups present in the sample.In some embodiments, a probe may include a binder coupled to HRP and asubstrate may include tyramine-coupled to a fluorophore.

Electron Transfer Reagents and Photoreaction

An electron transfer reagent may include one or more chemicals that canengage in a photoreaction with a molecule capable of undergoingphotoexcitation. The molecule capable of undergoing photoexcitation maybe a signal generator. An electron transfer reagent may be contactedwith the sample in the form of a solid, a solution, a gel, or asuspension.

In some embodiments, an electron transfer reagent may include a boratesalt. In some embodiments, the borate salt is represented by thefollowing structural formula:

wherein:

-   -   each R₁, R₂, and R₃ is, independently, an alkyl, an alkenyl, an        akynyl, an aryl or a heteroaryl, wherein said alkyl, alkenyl,        alkynyl, aryl or heteroaryl is optionally substituted with one        or more substituents selected from the group consisting of        (C₁-C₄)alkyl, (C₁-C₄)alkoxy, (C₁-C₄)alkylamino, amino, hydroxyl,        cyano, halogen, or nitro.    -   R₄ is an alkyl, an alkenyl, or an akynyl, wherein said alkyl,        alkenyl, or alkynyl is optionally substituted with one or more        substituents selected from the group consisting of (C₁-C₄)alkyl,        (C₁-C₄)alkoxy, (C₁-C₄)alkylamino, amino, hydroxyl, cyano,        halogen, or nitro, and    -   M⁺ is selected from the group consisting of inorganic cations        and organic cations.

In some embodiments, M⁺ is selected from the group of inorganic cations,e.g., Li⁺, Na⁺, or K⁺. In other embodiments, M⁺ is selected from thegroup of inorganic cations. Non-limiting examples of organic cations caninclude NR₄ ⁺, wherein each R is independently hydrogen, a substitutedor unsubstituted alkyl group (e.g., a hydroxyalkyl group, aminoalkylgroup or ammoniumalkyl group) or substituted or unsubstituted aryl group(e.g., phenyl, naphthyl, and anthracyl, imidazolyl, thienyl, furanyl,pyridyl, pyrimidyl, pyranyl, pyrazolyl, pyrroyl, pyrazinyl, thiazole,oxazolyl, and tetrazole).

In some embodiments, each R₁, R₂, and R₃ is aryl. In some embodiments,said aryl is phenyl. In some embodiments, said phenyl is anunsubstituted phenyl.

In some embodiments, R₄ is an optionally substituted alkyl. In someembodiments, R₄ is unsubstituted butyl.

In some embodiments, each R₁, R₂, and R₃ is an optionally substitutedaryl and R₄ is an optionally substituted alkyl. In a further embodiment,each R₁, R₂, and R₃ is unsubstituted phenyl and R₄ is unsubstitutedbutyl, and the borate salt is triphenylbutyl borate salt.

In some embodiments, M⁺ is an inorganic cation. In some embodiments, theinorganic cation is Li⁺, Na⁺ or K⁺. In one embodiment, M⁺ is Li⁺.

Other suitable electron transfer reagents may include sulfinates,enolates, carboxylates (e.g., ascorbic acid), organometallics and amines(e.g., triethanolamine, and N-phenylglycine). These and other electrontransfer reagents have been previously described (see, e.g.,Macromolecules 1974, 7, 179-187; Photogr. Sci. Eng. 1979, 23, 150-154;Topics in Current Chemistry, Mattay, J., Ed.; Springer-Verlag: Berlin,1990, Vol. 156, pp 199-225; and Pure Appl. Chem. 1984, 56, 1191-1202.)

An electron transfer reagent to be used for photoactivated chemicalbleaching is chosen such that the photoreaction between the electrontransfer reagent and a signal generator is energetically favorable. Insome embodiments, the electron transfer reagent and the photoexcitedsignal generator form an electron donor/acceptor pair, wherein anelectron transfer from the electron transfer reagent to the signalgenerator is energetically favorable. The electron transfer may furtherlead to chemical modification of the signal generator, resulting inbleaching of the signal generator. Examples of electron transferreagents and signal generators that can form electron donor/acceptorpairs include triaryl alkyl borates, such as triphenyl butyl borate asan electron transfer reagent and cyanine dyes (e.g., Cy3 and Cy5),BODIPY, rhodamine or acridone dyes as signal generators.

One or more of the aforementioned electron transfer reagents may be usedin the methods disclosed herein depending upon susceptibility of thesignal generator, of the enzyme, of the binder, of the target, or of thebiological sample to photoexcitation and/or subsequent photoreactionwith the electron transfer reagent. In some embodiments, photoexcitationof the signal generator by irradiation and subsequent photoreactionbetween the electron transfer reagent and the photoexcited signalgenerator essentially does not affect the integrity of the binder, thetarget, and the biological sample. In some embodiments, photoexcitationof the signal generator by irradiation and subsequent photoreaction doesnot affect the specificity of binding between the binder and the target.

In some embodiments, where two or more (up to 5) signal generators maybe employed simultaneously, a photoreaction may be capable ofselectively modifying one or more signal generators. This selectivitymay be derived from selective photoexcitation of the signal generator byirradiation at specific wavelength. The irradiation wavelength is chosensuch that one or more signal generator may photoexcited, while theremaining one or more signal generator that may be present in a samplemay remain unaffected. In some embodiments, irradiation limited to arange of wavelengths between 520-580 nm can be used for selectivephotoexciation of a Cy3 dye. In other embodiments, irradiation limitedto a range of wavelengths between 620-680 nm can be used for selectivephotoexcitation of a Cy5 dye. In alternative embodiments, selectivephotoexcitation may be accomplished by using a laser.

The propensity of photoexcited signal generators to further undergophotoreaction may depend on the choice of the electron transfer reagent,as discussed above, as well as on the reaction conditions, such astemperature, solvent and pH.

In some embodiments, the photoactivated chemical bleaching is carriedout at a temperature of 4-50° C., more preferably, at a temperature of20-30° C.

In some embodiments, the photoactivated chemical bleaching is carriedout in a solution. In some embodiments, the solution is a bufferedsolution. In a further embodiment, the buffered solution is the solutionbuffered in phosphate buffered saline (PBS). In some embodiments, thesolution is buffered at pH of 5-9. In a preferred embodiment, the pH ofthe solution is 6-8.

Sequentially Analyzing a Biological Sample, Contacting and Binding theProbe

A biological sample may be contacted with a probe to bind the probe to atarget in the biological sample. In some embodiments, a target may notbe easily accessible for binding with the probe and a biological samplemay be further processed to facilitate the binding between the targetand the binder in the probe, for example through antigen recovery,enzymatic digestion, epitope retrieval, or blocking.

In some embodiments, a probe may be contacted with the biological samplein the form of a solution. In some embodiments, a probe may include abinder coupled to a label (signal generator or an enzyme). The binderand the label (signal generator or enzyme) may be embodied in a singlemolecule and the probe solution may be applied in a single step.Alternatively, the binder and the label (signal generator or enzyme) maybe distinct entities and the probe solution may be applied in a singlestep or multiple steps. In all embodiments, a control probe may furtherbe bonded to one or more targets in the sample.

Depending on the nature of the binder, the target, and the bindingbetween the two, sufficient contact time may be allowed. In someembodiments, an excess of probe molecules (and accordingly bindermolecules) may be employed to ensure all the targets in the biologicalsample are bound. After a sufficient time has been provided for thebinding action, the sample may be contacted with a wash solution (forexample, an appropriate buffer solution) to wash away any unboundprobes. Depending on the concentration and type of probes used, abiological sample may be subjected to a number of washing steps with thesame or different washing solutions being employed in each step.

In some embodiments, the biological sample may be contacted with morethan one probe in the first binding step. The plurality of probes may becapable of binding different targets in the biological sample. Forexample, a biological sample may include two targets: target1 andtarget2 and two sets of probes may be used in this instance: probe1(having binder1 capable of binding to target1) and probe2 (havingbinder2 capable of binding to target2). The plurality of probes may alsocomprise a plurality of multiple sets of target-binding probes. Aplurality of probes may be contacted with the biological samplesimultaneously (for example, as a single mixture) or sequentially (forexample, a probe1 may be contacted with the biological sample, followedby washing step to remove any unbound probe1, followed by contacting aprobe2 with the biological sample, and so forth).

The number of probes that may be simultaneously bound to the target maydepend on the type of detection employed, that is, the spectralresolution achievable. For example, for fluorescence-based signalgenerators, up to five different probes (providing up to five spectrallyresolvable fluorescent signals) may be employed in accordance with thedisclosed methods. Spectrally resolvable, in reference to a plurality offluorescent signal generators, indicates that the fluorescent emissionbands of the signal generators are sufficiently distinct, that is,sufficiently non-overlapping, such that, binders to which the respectivesignal generators are attached may be distinguished on the basis of thefluorescent signal generated by the respective signal generators usingstandard photodetection systems. In some embodiments all probes may bysimultaneously bound but the sequentially detected in sets of 1-5 probesper cycle.

In some embodiments, a biological sample may be essentially contactedwith five or less than five probes in the first binding step. Inembodiments employing enzyme-based probes, the number of probes that maybe simultaneously bound to the target may also depend on the number ofdifferent enzymes and their corresponding substrates available.

In some embodiments, a biological sample may include a whole cell, atissue sample, or the biological sample may be adhered to a microarray,a gel, or a membrane. In some embodiments, a biological sample mayinclude a tissue sample. The tissue sample may be obtained by a varietyof procedures including, but not limited to surgical excision,aspiration or biopsy. The tissue may be fresh or frozen. In someembodiments, the tissue sample may be fixed and embedded in paraffin.The tissue sample may be fixed or otherwise preserved by conventionalmethodology; the choice of a fixative may be determined by the purposefor which the tissue is to be histologically stained or otherwiseanalyzed. The length of fixation may depend upon the size of the tissuesample and the fixative used. For example, neutral buffered formalin,Bouin's or paraformaldehyde, may be used to fix or preserve a tissuesample.

In some embodiments, the tissue sample may be first fixed and thendehydrated through an ascending series of alcohols, infiltrated andembedded with paraffin or other sectioning media so that the tissuesample may be sectioned. In an alternative embodiment, a tissue samplemay be sectioned and subsequently fixed. In some embodiments, the tissuesample may be embedded and processed in paraffin. Examples of paraffinthat may be used include, but are not limited to, Paraplast, Broloid,and Tissuemay. Once the tissue sample is embedded, the sample may besectioned by a microtome into sections that may have a thickness in arange of from about three microns to about five microns. Once sectioned,the sections may be attached to slides using adhesives. Examples ofslide adhesives may include, but are not limited to, silane, gelatin,poly-L-lysine. In embodiments, if paraffin is used as the embeddingmaterial, the tissue sections may be deparaffinized and rehydrated inwater. The tissue sections may be deparaffinized, for example, by usingorganic agents (such as, xylenes or gradually descending series ofalcohols).

In some embodiments, aside from the sample preparation proceduresdiscussed above, the tissue section may be subjected to furthertreatment prior to, during, or following immunohistochemistry. Forexample, in some embodiments, the tissue section may be subjected toepitope retrieval methods, such as, heating of the tissue sample incitrate buffer or Tris buffer or both in a sequential manner. In someembodiments, a tissue section may be optionally subjected to a blockingstep to minimize any non-specific binding.

In some embodiments, the biological sample or a portion of thebiological sample, or targets present in the biological sample may beadhered on the surface, e.g. DNA microarrays, or protein microarrays, oron the surface of solid supports (such as gels, blots, glass slides,beads, or ELISA plates). In some embodiments, targets present in thebiological sample may be adhered on the surface of solid supports.Targets in the biological sample may be adhered on the solid support byphysical bond formation, by covalent bond formation, or both.

In some embodiments, the targets in the biological sample may be adheredto membranes and probed sequentially using the methods disclosed herein.In some embodiments, targets in the biological sample may be processedbefore contacting the sample with the membrane. For example, embodimentsinvolving methods for probing protein targets in a tissue sample mayinclude the step of extracting the target proteins a biological sampleof tissue homogenate or an extract. Solid tissues or whole cells may befirst broken down mechanically using a blender (for larger samplevolumes), using a homogenizer (smaller volumes), or by sonication.Different cell compartments and organelles may be separated usingfiltration and centrifugation techniques. Detergents, salts, and buffersmay also be employed to encourage lysis of cells and to solubilizeproteins. Similarly, embodiments involving methods for probing nucleicacids may include the step of preparing DNA or RNA fragments, forexample using restriction endonucleases (for DNA).

In some embodiments, targets extracted from the biological sample may befurther separated by gel electrophoresis. Separation of targets may beby isoelectric point (pI), molecular weight, electric charge, or acombination of these factors. The nature of the separation may depend onthe treatment of the sample and the nature of the gel. A suitable gelmay be selected from a polyacrylamide gel, an SDS-polyacrylamide gel, oran agarose gel.

A suitable membrane may be selected such that the membrane hasnon-specific target binding properties. In some embodiments, a suitablemembrane may be selected from a polyvinylidene fluoride membrane, anitrocellulose membrane, or a nylon membrane. In some embodiment, asuitable membrane may be selected such that the membrane may besubstantially stable to multiple probing. In embodiments involvingprobing of targets using protein probes, the membranes may be blockedusing a blocking solution to prevent non-specific binding of proteinprobes to the membranes. In embodiments, involving probing of DNAfragments, the DNA gel may be treated with a dilute HCL solution or analkaline solution to facilitate more efficient transfer of the DNA fromthe gel to the membrane.

In some embodiments, the membrane may be subjected to temperatures in arange of about 60° C. to about 100° C. to covalently bind the targets tothe membrane, for example DNA targets to a nitrocellulose membrane. Insome embodiments, the membrane may be exposed to ultraviolet radiationto covalently bind the targets to the membrane, for example DNA targetsto a nylon membrane. In some embodiments, the targets in the biologicalsample may not be separated by electrophoresis before blotting on amembrane and may be probed directly on a membrane, for example, in dotblot techniques.

Following the preparation of the tissue sample or the membrane, a probesolution (e.g., labeled-antibody solution) may be contacted with thetissue section or the membrane for a sufficient period of time and underconditions suitable for binding of binder to the target (e.g., antigen).As described earlier, two detection methods may be used: direct orindirect. In a direct detection, a signal generator-labeled primaryantibody (e.g., fluorophore-labeled primary antibody or enzyme-labeledprimary antibody) may be incubated with an antigen in the tissue sampleor the membrane, which may be visualized without further antibodyinteraction. In an indirect detection, an unconjugated primary antibodymay be incubated with an antigen and then a labeled secondary antibodymay bind to the primary antibody. Signal amplification may occur asseveral secondary antibodies may react with different epitopes on theprimary antibody. In some embodiments two or more (at most five) primaryantibodies (from different species, labeled or unlabeled) may becontacted with the tissue sample. Unlabeled antibodies may be thencontacted with the corresponding labeled secondary antibodies. Inalternate embodiments, a primary antibody and specific bindingligand-receptor pairs (such as biotin-streptavidin) may be used. Theprimary antibody may be attached to one member of the pair (for examplebiotin) and the other member (for example streptavidin) may be labeledwith a signal generator or an enzyme. The secondary antibody, avidin,streptavidin, or biotin may be each independently labeled with a signalgenerator or an enzyme.

In embodiments where the primary antibody or the secondary antibody maybe conjugated to an enzymatic label, a fluorescent signalgenerator-coupled substrate may be added to provide visualization of theantigen. In some embodiments, the substrate and the fluorescent signalgenerator may be embodied in a single molecule and may be applied in asingle step. In other embodiments, the substrate and the fluorescentsignal generator may be distinct entities and may be applied in a singlestep or multiple steps.

An enzyme coupled to the binder may react with the substrate to catalyzea chemical reaction of the substrate to covalently bind the fluorescentsignal generator-coupled substrate the biological sample. In someembodiments, an enzyme may include horseradish peroxidase and thesubstrate may include tyramine. Reaction of the horseradish peroxidase(HRP) with the tyramine substrate may cause the tyramine substrate tocovalently bind to phenolic groups present in the sample. In embodimentsemploying enzyme-substrate conjugates, signal amplification may beattained as one enzyme may catalyze multiple substrate molecules. Insome embodiments, methods disclosed herein may be employed to detect lowabundance targets using indirect detection methods (e.g., usingprimary-secondary antibodies), using HRP-tyramide signal amplificationmethods, or combinations of both (e.g., indirect HRP-tyramide signalamplification methods). Incorporation of signal amplification techniquesinto the methods disclosed herein and correspondingly the type of signalamplification techniques incorporated might depend on the sensitivityrequired for a particular target and the number of steps involved in theprotocol.

Observing a Signal from the Probe or from the First Set of the Pluralityof Probes

A signal from the signal generator may be detected using a detectionsystem. The nature of the detection system used may depend upon thenature of the signal generators used. The detection system may includean, a charge coupled device (CCD) detection system a fluorescentdetection system, an electrical detection system, a photographic filmdetection system, a chemiluminescent detection system, an enzymedetection system, an optical detection system, a near field detectionsystem, or a total internal reflection (TIR) detection system.

One or more of the aforementioned techniques may be used to observe oneor more characteristics of a signal from a signal generator (coupledwith a binder or coupled with an enzyme substrate). In some embodiments,signal intensity, signal wavelength, signal location, signal frequency,or signal shift may be determined using one or more of theaforementioned techniques. In some embodiments, one or moreaforementioned characteristics of the signal may be observed, measured,and recorded.

In some embodiments, the observed signal is a fluorescent signal, and aprobe bound to a target in a biological sample may include a signalgenerator that is a fluorophore. In some embodiments, the fluorescentsignal may be measured by determining fluorescence wavelength orfluorescent intensity using a fluorescence detection system. In someembodiments, a signal may be observed in situ, that is, a signal may beobserved directly from the signal generator associated through thebinder to the target in the biological sample. In some embodiments, asignal from the signal generator may be analyzed within the biologicalsample, obviating the need for separate array-based detection systems.

In some embodiments, observing a signal may include capturing an imageof the biological sample. In some embodiments, a microscope connected toan imaging device may be used as a detection system, in accordance withthe methods disclosed herein. In some embodiments, a signal generator(such as, fluorophore) may be excited and the signal (such as,fluorescence signal) obtained may be observed and recorded in the formof a digital signal (for example, a digitalized image). The sameprocedure may be repeated for different signal generators (if present)that are bound in the sample using the appropriate fluorescence filters.

In some embodiments, multiple different types of signals may be observedin the same sample. For example, one target may be detected with afluorescent probe and a second target in the same sample may be detectedwith a chromogenic probe.

Applying an Electron Transfer Reagent and Irradiating to Initiate aPhotoreaction to Modify the Signal

To modify the signal, an electron transfer reagent may be applied to thesample, and the sample may subsequently be irradiated to initiate aphotoreaction. In some embodiments, signal modification may include achange in one or more signal characteristics, for example, a decrease inintensity of signal, a shift in the signal peak, or a change in theresonant frequency. In some embodiments, a photoreaction may modify thesignal by substantially inactivating, i.e., bleaching, the fluorescentsignal generator and the enzyme (if employed).

In some embodiments, an electron transfer reagent may be in the form ofa solution. In one embodiment, the electron transfer reagent is presentin the form of a buffered aqueous solution. In some embodiments, theelectron transfer reagent may be a borate salt. In further embodiments,the electron transfer reagent may be a lithium salt of a triphenyl butylborate present at a concentration of 0.001 mM to 1000 mM. In a preferredembodiment, the concentration of triphenyl butyl borate is from 20 mM to100 mM. In some embodiments, the concentration of the electron transferreagent, e.g., borate salt, may represent 1-60 equivalents of theconcentration of the signal generator, e.g., fluorescent dye.

Irradiation of the sample contacted with the electron transfer reagentmay be carried out for a predetermined amount of time. The duration ofirradiation may depend on the desired duration of the photoreactionbetween the electron transfer reagent and the photoexcited signalgenerator. In some embodiments, the irradiation step may be performedfor about 20 seconds to about 60 minutes, preferably for about 20seconds to about 15 minutes, and even more preferably, for about 20seconds to about 5 minutes. In some embodiments, the irradiation stepmay be performed until no residual signal is observed from the signalgenerator. In some embodiments, the irradiation step may be performed atroom temperature.

In some embodiments, the photoreaction is carried out at a temperatureof 4-50° C., more preferably, at a temperature of 20-30° C.

In some embodiments, the photoreaction is carried out in a solution. Insome embodiments, the solution is a buffered solution. In a furtherembodiment, the buffered solution is the solution buffered in phosphatebuffered saline (PBS). In some embodiments, the solution is buffered atpH of 5-9. In a preferred embodiment, the pH of the solution is 6-8.

In some embodiments, the conditions for a photoreaction (e.g.,irradiation wavelength) may be selected such that the binder, thetarget, the biological sample, and binding between the binder and thetarget may not be affected by the photoreaction. In some embodiments,the photoreaction may only affect the signal generator and the enzyme(if employed) and the electron transfer reagent, and may not affect thetarget/binder binding or the binder integrity. Thus, by way of example,a binder may include a primary antibody or a primary antibody/secondarycombination. A photoreaction according to the methods disclosed hereinmay only affect the signal generator, and the primary antibody orprimary antibody/secondary antibody combination may essentially remainunaffected. In some embodiments, a binder (such as, a primary antibodyor primary antibody/secondary antibody combination) may remain bound tothe target in the biological sample after contacting the sample with theelectron transfer reagent and subsequent irradiation to initiate aphotoreaction.

In some embodiments, a characteristic of the signal may be observedafter the photoreaction to determine the effectiveness of the signalmodification. For example, a color may be observed before thephotoreaction and the color may be absent after the photoreaction. Inanother example, fluorescence intensity from a fluorescent signalgenerator may be observed before the photoreaction and after thephotoreaction. In some embodiments, a decrease in signal intensity by apredetermined amount may be referred to as signal modification, orphotoactivated chemical bleaching, or bleaching. In some embodiments,modification of the signal, or photoactivated chemical bleaching, mayrefer to a decrease in the signal intensity by an amount in a range ofgreater than about 50 percent. In some embodiments, modification of thesignal, or photoactivated chemical bleaching, may refer to a decrease inthe signal intensity by an amount in a range of greater than about 60percent. In some embodiments, modification of the signal, orphotoactivated chemical bleaching, may refer to a decrease in the signalintensity by an amount in a range of greater than about 80 percent. Insome embodiments, modification of the signal, or photoactivated chemicalbleaching, may refer to a decrease in the signal intensity by an amountin a range of greater than about 90 percent. In some embodiments,modification of the signal, or photoactivated chemical bleaching, mayrefer to a decrease in the signal intensity by an amount in a range ofgreater than about 95 percent. In some embodiments, modification of thesignal, or photoactivated chemical bleaching, may refer to a decrease inthe signal intensity by an amount in a range of about 100 percent, or tocomplete bleaching.

Contacting the Sample with a Subsequent Probe and Binding to aSubsequent Target

The biological sample or the sample may be contacted with a subsequentprobe using one or more procedures described herein above for the firstprobe. The subsequent probe may be capable of binding to targetdifferent from the target bound in the earlier steps. In embodimentswhere a plurality of probes may be contacted with the biological samplein the earlier probe contact steps, the subsequent probe may be capableof binding a target different from the targets bound by the earlierprobe set. In some embodiments, a biological sample may be contactedwith a plurality of probes in the subsequent probe contact step. In someembodiments, where a plurality of multiple sets of probes was applied toa biological sample in the first step, a subsequent set of signals fromthe subsequent set of probes may be generated. Generation of the secondset of signals may comprise associating the second set of probes with aseparate moiety that comprises signal generator. For example, the secondset of probes may comprise a biotin tag, and the moiety comprisingsignal generator may also comprise streptavidin capable of binding thebiotin tag. Alternatively, generation of the second set of signals maycomprise un-masking the signal-generating moiety, e.g., by modifying thedistance between the fluorophore-quencher pair. In some embodimentsgeneration of the second set of signals may be by hybridization oflabeled probes complementary to sequences attached to the second set ofprobes.

In embodiments where binders coupled to enzymes may be employed asprobes, binding steps may further include reacting steps involvingreaction of the enzyme with an enzyme substrate coupled to fluorescentsignal generator.

In some embodiments, the signal generator (e.g., a fluorescent signalgenerator) used in the different binding steps may be the same, that is,detectable in the same detection channel. Methods employing the samesignal generator in different binding steps may allow for detection ofmultiple targets when limited number of detection channels areavailable. In some embodiments, where a set of probes (2 to 5 probes)may be employed in the first binding step, the subsequent probes mayinclude the same signal generators as in the earlier binding steps. Forexample, a first binding step may include Cy3, Cy5, and Cy7-conjugateddifferent binders. In some embodiments, the subsequent binding steps mayalso include the same dye set, that is, Cy3, Cy5, and Cy7.

In some embodiments, the signal generator (e.g., a fluorescent signalgenerator) used in the different binding steps may be different, thatis, independently detectable in different detection channels. Forexample, in some embodiments, a first probe may include a Cy3 dye, whichhas a fluorescent emission wavelength in the green region and asubsequent probe may include a Cy7 dye, which has a fluorescent emissionwavelength in the near infrared region.

In embodiments employing binder-coupled enzymes as probes, the enzymesand the substrates employed in the different binding and reacting stepsmay be the same. An earlier enzyme may be inactivated in the course of aphotoreaction or in a separate inactivation step before binding thesample to a subsequent enzyme to prevent cross-reaction of the earlierenzyme with the subsequent substrate. For example, a first binding andreacting step may include binder coupled to HRP and tyramine coupled toa first fluorophore. The photoinduced chemical bleaching step mayinvolve the steps of substantially inactivating the fluorophore andsubstantially inactivating the HRP. In some embodiments, photoinducedchemical bleaching and inactivation steps may occur simultaneously. Insome embodiments, photoinduced chemical bleaching and inactivation stepsmay occur sequentially. After the photoinduced chemical bleaching andinactivation steps, the sample may be contacted with a subsequent bindercoupled to HRP, which may be further reacted with tyramine coupled to asecond fluorophore. Similarly, the subsequent binding and reacting stepsmay be affected using multiple iterations of HRP-tyramine as enzymesubstrate conjugates, each binding and reacting step followed by thephotoinduced chemical bleaching and inactivation step. The firstfluorophore and the subsequent fluorophores may be the same or differentdepending on the number of detection channels available for detection.

In some embodiments, the first binding step may include a set of probes(e.g., 2 to 5 probes), each probe including a binder capable of bindingto a different target and each enzyme capable of catalyzing a chemicalreaction of a different substrate. For example, in one embodiment, thefirst probe set may include a binder1 coupled to HRP and a binder2coupled to AP. The reacting step may include contacting the sample withtyramine-coupled to Cy3 and NADP-coupled to Cy7. Following reaction ofthe enzymes with their corresponding substrates and observing thesignals, the cyanine dyes may be inactivated by photoinduced chemicalbleaching and the enzymes inactivated in the course of a photoreactionor by addition of a suitable inactivating agent. The subsequent probingsteps may include the same set of binder-enzyme andsubstrate-fluorophore pairs or different set of binder-enzyme andsubstrate-fluorophore pairs. The plurality of probes and thesubstrate-signal generator may be contacted with the biological samplesimultaneously (for example, as a single mixture) or sequentially (forexample, a probe1 may be contacted with the biological sample, followedby washing step to remove any unbound probe1, followed by contacting aprobe2 with the biological sample, and so forth).

Observing a Subsequent Signal from a Subsequent Probe

One or more detection methods described hereinabove may be used toobserve one or more characteristics of a subsequent (e.g., second,third, etc.) signal from a subsequent signal generator (present in thesubsequent probe). In some embodiments, signal intensity, signalwavelength, signal location, signal frequency, or signal shift may bedetermined using one or more of the aforementioned techniques. Similarto the first signal, a subsequent signal (for example, a fluorescencesignal) obtained may be recorded in the form of a digital signal (forexample, a digitalized image). In some embodiments, observing asubsequent signal may also include capturing an optical image of thebiological sample.

Reiteration of the Contacting, Binding, and Observing Steps

In some embodiments, after contacting the sample with a subsequent(e.g., second, third, etc.) probe, bleaching of the signal generator ina photoreaction, and subsequent probe administration signal generationfrom already bound probes may be repeated multiple times. In someembodiments, after observing a second signal from the second probe, thebiological sample may be contacted with an electron transfer reagent andirradiated to modify the signal from the second probe. Furthermore, athird probe may be contacted with the biological sample, wherein thethird probe may be capable of binding a target different from the firstand the second probes. Likewise, a signal from the third probe may beobserved and followed by application of electron transfer reagent andirradiation to modify the signal. The binding, observing, and bleachingsteps may be repeated iteratively multiple times using an n^(th) probecapable of binding to additional targets to provide the user withinformation about a variety of targets using a variety of probes and/orsignal generators. In embodiments where binders coupled to enzymes maybe employed as probes, binding steps may further include reacting stepsinvolving reaction of the enzyme with an enzyme substrate coupled tofluorescent signal generator.

In some embodiments, the bleaching, binding, reacting (if applicable),and observing steps may be repeated one or more time. In someembodiments, the bleaching, binding, reacting (if applicable), andobserving steps may be repeated at least 5, at least 15, at least 30, atleast 60 times, at least 100 times, or at least 150 times. In someembodiments, the series of steps may be repeated 25-30 times. In otherembodiments, the series of steps may be repeated 2-10 times.

In some embodiments, a series of probes may be contacted with thebiological sample in a sequential manner to obtain a multiplexedanalysis of the biological sample. In some embodiments, a series ofprobe sets (including at most 5 probes in one set may be contacted withthe biological sample in a sequential manner to obtain a multiplexedanalysis of the biological sample. Multiplexed analysis generally refersto analysis of multiple targets in a biological sample using the samedetection mechanism.

In some embodiments, where a biological sample is contacted with aplurality of multiple sets of probes in the first step, a series ofsteps comprising bleaching, generating signals from a subsequent set ofprobes and observing the signal may be repeated at least 5, at least 15,at least 30, at least 60 times, at least 100 times, or at least 150times. In some embodiments, the series of steps may be repeated 25-30times. In other embodiments, the series of steps may be repeated 2-10times.

In some embodiments, the components of a biological sample are notsignificantly modified after repeated cycles the bleaching, binding,reacting (if applicable), and signal observing steps. In someembodiments, the components of a biological sample are not significantlymodified during the bleaching step. In some embodiments, the componentsof the biological sample that are not significantly modified during thebleaching step are targets. In some embodiments, more than 80% oftargets are not significantly modified in the course of the bleachingstep. In some embodiments, more than 95% of targets are notsignificantly modified in the course of the bleaching step.

Contacting the Sample with One or More Morphological Stain

In some embodiments, a biological sample may include a cell or a tissue,and the sample may be contacted with a morphological stain before,during, or after the contacting step with the first probe or subsequentprobe. A morphological stain may include a dye that may stain differentcellular components, in order to facilitate identification of cell typeor disease status. In some embodiments, the morphological stain may bereadily distinguishable from the signal generators in the probes, thatis, the stain may not emit signal that may overlap with signal from theprobe. For example, for a fluorescent morphological stain, the signalfrom the morphological stain may not autofluoresce in the samewavelength as the fluorophores used in the probes.

A morphological stain may be contacted with the biological samplebefore, during, or after, any one of the aforementioned steps. In someembodiments, a morphological stain may be contacted with biologicalsample along with the first probe contact step. In some embodiments, amorphological stain may be contacted with the biological sample beforecontacting the sample with an electron transfer reagent and irradiatedafter binding the first probe to the target. In some embodiments, amorphological stain may be contacted with a biological sample aftercontacting the sample with an electron transfer reagent and irradiationto modify the signal. In some embodiments, a morphological stain may becontacted with a biological sample along with the second probe contactstep. In some embodiments, a biological sample may be contacted with themorphological stain after binding the second probe to the target. Insome embodiments, where the morphological stains may result inbackground noise for the fluorescent signal from the signal generator,the morphological stains may be contacted with the biological sampleafter the probing, bleaching and reprobing steps. For example,morphological stains like H&E may be sequentially imaged and registeredafter the methods disclosed herein.

In some embodiments, chromophores, fluorophores, or enzyme/enzymesubstrates may be used as morphological stains. Suitable examples ofchromophores that may be used as morphological stains (and their targetcells, subcellular compartments, or cellular components) may include,but are not limited to, Hematoxylin (nucleic acids), Orange G (redblood, pancreas, and pituitary cells), Light Green SF (collagen),Romanowsky-Giemsa (overall cell morphology), May-Grunwald (blood cells),Blue Counterstain (Trevigen), Ethyl Green (CAS) (amyloid),Feulgen-Naphthol Yellow S (DNA), Giemsa (differentially stains variouscellular compartments), Methyl Green (amyloid), pyronin (nucleic acids),Naphthol-Yellow (red blood cells), Neutral Red (nuclei), Papanicolaoustain (a mixture of Hematoxylin, Orange G and Bismarck Brown mixture(overall cell morphology)), Red Counterstain B (Trevigen), RedCounterstain C (Trevigen), Sirius Red (amyloid), Feulgen reagent(pararosanilin) (DNA), Gallocyanin chrom-alum (DNA), Gallocyaninchrom-alum and Naphthol Yellow S (DNA), Methyl Green-Pyronin Y (DNA),Thionin-Feulgen reagent (DNA), Acridine Orange (DNA), Methylene Blue(RNA and DNA), Toluidine Blue (RNA and DNA), Alcian blue(carbohydrates), Ruthenium Red (carbohydrates), Sudan Black (lipids),Sudan IV (lipids), Oil Red-O (lipids), Van Gieson's trichrome stain(acid fuchsin and picric acid mixture) (muscle cells), Masson trichromestain (hematoxylin, acid fuchsin, and Light Green mixture) (stainscollagen, cytoplasm, nucleioli differently), Aldehyde Fuchsin (elastinfibers), or Weigert stain (differentiates reticular and collagenousfibers).

Examples of suitable fluorescent morphological stains (and their targetcells, subcellular compartments, or cellular components if applicable)may include, but are not limited to: 4′,6-diamidino-2-phenylindole(DAPI) (nucleic acids), Hoechst 33258 and Hoechst 33342 (twobisbenzimides) (nucleic acids), Propidium Iodide (nucleic acids),Spectrum Orange (nucleic acids), Spectrum Green (nucleic acids),Quinacrine (nucleic acids), Fluorescein-phalloidin (actin fibers),Chromomycin A 3 (nucleic acids), Acriflavine-Feulgen reaction (nucleicacid), Auramine O-Feulgen reaction (nucleic acids), Ethidium Bromide(nucleic acids). Niss1 stains (neurons), high affinity DNA fluorophoressuch as POPO, BOBO, YOYO and TOTO and others, and Green FluorescentProtein fused to DNA binding protein, such as histones, ACMA, Quinacrineand Acridine Orange.

Examples of suitable enzymes (and their primary cellular locations oractivities) may include, but are not limited to, ATPases (musclefibers), succinate dehydrogenases (mitochondria), cytochrome c oxidases(mitochondria), phosphorylases (mitochondria), phosphofructokinases(mitochondria), acetyl cholinesterases (nerve cells), lactases (smallintestine), acid phosphatases (lysosomes), leucine aminopeptidases(liver cells), dehydrogenases (mitochondria), myodenylate deaminases(muscle cells), NADH diaphorases (erythrocytes), and sucrases (smallintestine).

In some embodiments, a morphological stain may be stable towardsphotoactivated chemical bleaching, that is, the signal generatingproperties of the morphological stain may not be substantially affectedby a photoreaction comprising contacting the morphological stain with anelectron transfer reagent and subsequent irradiation. In someembodiments, where a biological sample may be stained with a probe and amorphological stain at the same time, a bleaching of the signal from theprobe may not modify the signal from the morphological stain. In someembodiments, a morphological stain may be used as a control toco-register the molecular information (obtained through the iterativeprobing steps) and the morphological information (obtained through themorphological stains). In some embodiments, the morphological stain isnot modified by the electron transfer reagent upon irradiation of thesample.

Contacting the Sample with One or More Control Probe

In some embodiments, a control probe may be bonded to one or moretargets in the biological sample. In some embodiments, a control probemay be bonded to the targets along with the first probe contact step. Insome embodiments, a control probe may be applied to the biologicalsample simultaneously with the first probe. In some embodiments, acontrol probe may be applied to the biological sample sequentially, thatis before or after the application of the first probe, but beforeapplication of the electron transfer reagent and subsequent irradiation.

A control probe may include a signal generator that is stable towardsphotoactivated chemical bleaching or the signal generating properties ofthe signal generator are not substantially effected when contacted withthe electron transfer reagent and subsequent irradiation. A signalgenerator may include a radioisotope that is stable during exposure toan electron transfer reagent and irradiation or a fluorophore that isnot chemically modified upon exposure to an electron transfer reagentand irradiation. A suitable radioisotope may include P³², ³H, ¹⁴C, ¹²⁵Ior ¹³¹I. A suitable fluorophore may include DAPI.

In some embodiments, a suitable signal generator may be coupled to abinder to form a control probe. For example, a radioactive label may becoupled to an antibody to form a control probe and the antibody may bindto one or more target antigens present in the biological sample. Inother embodiments, a suitable signal generator may be capable of bindingto one more targets in the sample and also providing a detectablesignal, which is stable in the presence of the electron transfer reagentand during irradiation. For example, a suitable control probe may beDAPI, which is capable of binding to nucleic acids in the sample andalso capable of providing a fluorescent signal that is substantiallystable to photoactivated chemical bleaching, i.e., that is notsubstantially modified after addition of an electron transfer reagentand subsequent irradiation.

In some embodiments, a control probe may be employed in the methodsdisclosed herein to provide an indication of the stability of thetargets to the iterative staining steps. For example, a control probemay be bonded to a known target in the sample and a signal from thecontrol observed and quantified. The control signal may be thenmonitored during the iterative staining steps to provide an indicationof the stability of the targets or binders to the electron transferreagent and subsequent irradiation. In some embodiments, a quantitativemeasure (for example, signal intensity) of the control signal may bemonitored to quantify the amount of targets present in the sample afterthe iterative probing steps.

In some embodiments, a control probe may be employed to obtainquantitative information of the sample of interest, for exampleconcentration of targets in the sample or molecular weight of thetargets in the sample. For example, a control target (having knownconcentration or known molecular weight) may be loaded along with thesample of interest in a blotting technique. A control probe may bebonded to the control target and a control signal observed. The controlsignal may be then correlated with the signals observed from the sampleof interest using methods described herein below.

In some embodiments, a control probe may be employed in the methodsdisclosed herein to provide for co-registration of multiple molecularinformation (obtained through the iterative probing steps) and themorphological information (obtained, e.g., using DAPI). In someembodiments, methods disclosed herein may include co-registration ofmultiple fluorescent images with the bright-field morphological imagesobtained e.g., using H&E. In some embodiments, the probes employed inthe iterative probing steps may not have any common compartmentalinformation that may be used to register with the H&E images. A controlprobe like a DAPI nuclear stain may be employed to co-register thenucleus stained with hematoxylin in the bright-field images with thefluorescent images. The fluorescent images and the bright-field imagesmay be co-registered using image registration algorithms that may begrouped in two categories: intensity-based and feature-based techniques.

Correlating the First Signal and the Subsequent Signals

In some embodiments, a first signal, a subsequent signal, or the firstsignal and the subsequent signals may be analyzed to obtain informationregarding the biological sample. For example, in some embodiments, apresence or absence of a first signal may indicate the presence orabsence of the first target (capable of binding to the first binder) inthe biological sample. Similarly, the presence or absence of a secondsignal may indicate the presence or absence of the second target(capable of binding to the second binder in the biological sample). Inembodiments where multiple targets may be analyzed using a plurality ofprobes, the presence or absence of a particular signal may indicate thepresence or absence of corresponding target in the biological sample.

In some embodiments, the observing steps may include a quantitativemeasurement of at least one target in the sample. In some embodiments,an intensity value of a signal (for example, fluorescence intensity) maybe measured and may be correlated to the amount of target in thebiological sample. A correlation between the amount of target and thesignal intensity may be determined using calibration standards. In someembodiment, intensity values of the first and second signals may bemeasured and correlated to the respective target amounts. In someembodiments, by comparing the two signal intensities, the relativeamounts of the first target and the second target (with respect to eachother or with respect to a control) may be ascertained. Similarly, wheremultiple targets may be analyzed using multiple probes, relative amountsof different targets in the biological sample may be determined bymeasuring different signal intensities. In some embodiments, one or morecontrol samples may be used as described hereinabove. By observing apresence or absence of a signal in the samples (biological sample ofinterest versus a control), information regarding the biological samplemay be obtained. For example by comparing a diseased tissue sampleversus a normal tissue sample, information regarding the targets presentin the diseased tissue sample may be obtained. Similarly by comparingsignal intensities between the samples (i.e., sample of interest and oneor more control), information regarding the expression of targets in thesample may be obtained.

In some embodiments, the observing steps include co-localizing at leasttwo targets in the sample. Methods for co-localizing targets in a sampleare described in U.S. patent application Ser. No. 11/686,649, entitled“System and Methods for Analyzing Images of Tissue Samples”, filed onMar. 15, 2007; U.S. patent application Ser. No. 11/500,028, entitled“System and Method for Co-Registering Multi-Channel Images of a TissueMicro Array”, filed on Aug. 7, 2006; U.S. patent application Ser. No.11/606,582, entitled “System and Methods for Scoring Images of a TissueMicro Array, filed on Nov. 30, 2006, and U.S. application Ser. No.11/680,063, entitled Automated Segmentation of Image Structures, filedon Feb. 28, 2007, now U.S. Pat. No. 8,036,462, issued on Oct. 11, 2011,each of which is herein incorporated by reference.

In some embodiments, a location of the signal in the biological samplemay be observed. In some embodiments, a localization of the signal inthe biological signal may be observed using morphological stains. Insome embodiments relative locations of two or more signals may beobserved. A location of the signal may be correlated to a location ofthe target in the biological sample, providing information regardinglocalization of different targets in the biological sample. In someembodiments, an intensity value of the signal and a location of thesignal may be correlated to obtain information regarding localization ofdifferent targets in the biological sample. For examples certain targetsmay be expressed more in the cytoplasm relative to the nucleus, or viceversa. In some embodiments, information regarding relative localizationof targets may be obtained by comparing location and intensity values oftwo or more signals.

In embodiments employing blotting techniques, the observing steps mayinclude observing a location of the signal on the blot. The location ofthe signal in the blot may be then correlated with calibration standardsloaded along with the sample in the gel to obtain information regardingthe molecular weight of the targets in the different bands. In someembodiments, a location of the signal on the blot may be correlated to amolecular weight of the target and the isoelectric point of the target,e.g., in 2D-PAGE. In some embodiments, structural proteins such as actinor tubulin may be probed using control probes in western blots toquantify the amount of targets in the sample.

In some embodiments, one or more of the observing or correlating stepmay be performed using computer-aided means. In embodiments where thesignal(s) from the signal generator may be stored in the form of digitalimage(s), computer-aided analysis of the image(s) may be conducted. Insome embodiments, images (e.g., signals from the probe(s) andmorphological stains) may be overlaid using computer-aidedsuperimposition to obtain complete information of the biological sample,for example topological and correlation information.

In some embodiments, one or more of the aforementioned may be automatedand may be performed using automated systems. In some embodiments, allthe steps may be performed using automated systems.

The methods disclosed herein may find applications in analytic,diagnostic, and therapeutic applications in biology and in medicine. Insome embodiments, the methods disclosed herein may find applications inhistochemistry, particularly, immunohistochemistry. Analysis of cell ortissue samples from a patient, according to the methods describedherein, may be employed diagnostically (e.g., to identify patients whohave a particular disease, have been exposed to a particular toxin orare responding well to a particular therapeutic or organ transplant) andprognostically (e.g., to identify patients who are likely to develop aparticular disease, respond well to a particular therapeutic or beaccepting of a particular organ transplant). The methods disclosedherein, may facilitate accurate and reliable analysis of a plurality(e.g., potentially infinite number) of targets (e.g., disease markers)from the same biological sample.

EXAMPLES

The following examples are intended only to illustrate methods andembodiments in accordance with the invention, and as such should not beconstrued as imposing limitations upon the claims.

Example 1 Photoactivated Chemical Bleaching of Cyanine Dyes: DoseResponse

To a solution of Cy3 in PBS, 2-60 equivalents of triphenylbutyl boratelithium salt were added, and the solution was irradiated for 4 minutesor for 10 minutes. Absorbance at 550 nm was measured to monitorphotoactivated chemical bleaching, and the results were plotted, as isshown in FIG. 1. The solid line with squares represents A550 absorbanceafter Cy3 dye was irradiated for 4 minutes in the presence of differentconcentrations of triphenylbutyl borate. The solid line with diamondsrepresents A550 absorbance after Cy3 dye was irradiated for 10 minutesin the presence of different concentrations of triphenylbutyl borate.The results demonstrate that the extent of Cy3 bleaching increases withincreasing concentration of the borate salt.

Example 2 Comparison of Cy3 Bleaching by Photoreaction and ThermalOxidation

Three methods for bleaching Cy3 were compared. For the photoactivatedchemical bleaching reaction, Cy3 was mixed with triphenylbutylboratelithium salt and irradiated for 20 seconds. For the thermal oxidationreaction, Cy3 was mixed with basic hydrogen peroxide and incubated for20 seconds. For the control reaction, Cy3 was incubated with water for20 seconds. The color of the Cy3 solution in all three reactions wascompared before and after each incubation and/or reaction. Shown in FIG.2 is the grayscale image of the vials containing the thermal oxidationreaction, the photoactivated chemical bleaching reaction and the controlreaction before and after completion of bleaching. The control reactiondoes not change its dark pink color (vial shown in the center). Thecolor of the thermal oxidation reaction changes from dark pink to lightpink after 20 seconds of thermal oxidation (vial shown on the right).The photoactivated chemical bleaching reaction turns from dark pink tocolorless after 20 seconds of irradiation (vial shown on the left).

Example 3 Photoactivated Chemical Bleaching of Cy3 and Cy5 in Tissues

Tissue Microarrays (TMA, Pantomics Catalog No. MTU541C) were stainedwith Cy3-conjugated cytokeratin and Cy5-conjugated pan-cadherin.Photoactivated chemical bleaching of the Cy3 and Cy5 was accomplished byincubating stained TMAs with triphenylbutylborate lithium salt andirradiation for 2 minutes. Images were taken on the Olympus Microscopebefore and after bleaching. Images of samples stained withCy3-conjugated cytokeratin before and after bleaching are shown in FIG.3. Images of samples stained with Cy3-conjugated cytokeratin before andafter bleaching are shown in FIG. 4. This data demonstrates thatphotoactivated chemical bleaching effectively destroys Cy3 and Cy5signals in stained tissues.

Example 4 Photoactivated Chemical Bleaching of BODIPY

The photoactivated chemical bleaching reaction of BODIPY was carried outin methanol/water without or with 100 mM solution of triphenylbutylborate lithium salt. Irradiation of both samples was carried out for 2minutes using 100 W halogen lamp. FIG. 5 shows the grayscale image ofthe vials containing BODIPY and triphenylbutyl borate salt before andafter irradiation. The bright yellow color of the reaction becomesyellowish after irradiation. Also shown in FIG. 5 is the fluorescencespectrum of the reaction before irradiation (unevenly broken line) andafter irradiation (solid line). The fluorescence spectrum demonstratescomplete fluorescence quenching of BODIPY by photoactivated chemicalbleaching.

Example 5 Photoactivated Chemical Bleaching of Rhodamine

The photoactivated chemical bleaching reaction of rhodamine was carriedout in methanol/water without or with 100 mM solution oftriphenylbutylborate lithium salt. Irradiation of both samples wascarried out for 2 minutes using 100 W halogen lamp. FIG. 6 shows thegrayscale image of the vials containing rhodamine and triphenylbutylborate salt before and after irradiation. The bright red color of thereaction is lost after irradiation. Also shown in FIG. 6 is thefluorescence spectrum of the reaction before irradiation (unevenlybroken line) and after irradiation (solid line). The fluorescencespectrum demonstrates complete fluorescence quenching of rhodamine byphotoactivated chemical bleaching.

Example 6 Photoactivated Chemical Bleaching of1,3-Dichloro-7-Hydroxy-9,9-Dimethyl-2(9H)-Acridinone (DDAO)

The photoactivated chemical bleaching reaction of acridone was carriedout in methanol/water without or with 100 mM solution oftriphenylbutylborate lithium salt. Irradiation of both samples wascarried out for 2 minutes using 100 W halogen lamp. FIG. 7 shows thegrayscale image of the vials containing DDAO and triphenylbutyl boratesalt before and after irradiation. The brown color of the reactionbecomes yellow is lost after irradiation. Also shown in FIG. 7 is thefluorescence spectrum of the reaction before irradiation (unevenlybroken line), after 1 irradiation (solid line) and after 2 minuteirradiation (evenly broken line). The fluorescence spectrum alsodemonstrates incomplete fluorescence quenching of DDAO in the limitedtime used for irradiation.

What is claimed is:
 1. A method of probing multiple targets in abiological sample comprising: (a) providing a biological samplecontaining multiple targets; (b) binding at least one probe to thebiological sample and wherein said probe comprises a binder and at leastone of a optical signal generator or a fluorescent signal generator andwherein the binder is capable of binding specifically to one or moretargets in the biological sample; (c) observing a signal from the atleast one probe bound in step (b); (d) contacting the biological samplecomprising the bound probe of step (b) with an electron transferreagent, wherein the electron transfer reagent is a borate saltrepresented by the following structural formula:

wherein: each R₁, R₂, and R₃ is, independently, an alkyl, an alkenyl, anakynyl, an aryl or a heteroaryl, wherein said alkyl, alkenyl, alkynyl,aryl or heteroaryl is optionally substituted with one or moresubstituents selected from the group consisting of (C1-C4)alkyl,(C1-C4)alkoxy, (C1-C4)alkylamino, amino, hydroxyl, cyano, halogen, ornitro: R₄ is an alkyl, an alkenyl, or an akynyl, wherein said alkyl,alkenyl, or alkynyl is optionally substituted with one or moresubstituents selected from the group consisting of (C1-C4)alkyl,(C1-C4)alkoxy, (C1-C4)alkylamino amino, hydroxyl, cyano, halogen, ornitro: and M⁺ is selected from the group consisting of organic andinorganic cations; (e) irradiating the biological sample of step (d);(f) binding at least one probe to one or more targets present in thesample of step (e); and (g) observing a signal from the probe bound instep (f).
 2. The method of claim 1, wherein the probe in step (b)comprises an optical signal generator, and the signal observed in step(c) is an optical signal.
 3. The method of claim 2, wherein the probe instep (b) comprises a fluorescent signal generator, and the signalobserved in step (c) is a fluorescent signal.
 4. The method of claim 1,wherein irradiating the sample in step (e) is carried out in thepresence of a buffer at pH of 5-9.
 5. The method of claim 1, whereinsteps (d) and (e) are carried out at the temperature of 4-50° C.
 6. Themethod of claim 1, wherein irradiating the sample in step (e) isaccomplished by exposing the sample to light of 350 nm-1.3 μM inwavelength.
 7. The method of claim 6, wherein irradiating the sample instep (e) is accomplished by exposing the sample to light of 400-700 nmin wavelength.
 8. The method of claim 1, wherein each R₁, R₂, and R₃ isan optionally substituted aryl and R₄ is an optionally substitutedalkyl.
 9. The method of claim 8, wherein each R₁, R₂, and R₃ isunsubstituted phenyl and R₄ is unsubstituted butyl, and the borate saltis triphenylbutyl borate salt.
 10. The method of claim 1, wherein M⁺ isan inorganic cation selected from the group consisting of Li⁺, Na⁺ orK⁺.
 11. The method of claim 3, wherein the fluorescent signal generatorcomprises a cyanine dye.
 12. The method of claim 11, wherein the cyaninedye is Cy3 or Cy5.
 13. The method of claim 1, wherein steps (d)-(g) arerepeated one or more times.
 14. The method of claim 1, wherein the steps(d) and (e) are performed for about 20 seconds to about 15 minutes. 15.The method of claim 1, further comprising measuring one or moreintensity values of the signal observed in observing step (c), step (g),or steps (c) and (g).
 16. The method of claim 15, further comprisingcorrelating the intensity value with an amount of target present in thesample.
 17. The method of claim 1, wherein the probe in step (b) and theprobe in step (f) each comprise a signal generator, wherein the signalgenerator in step (b) is different from the signal generator in step(f).